yes oh hello I was just reading some uh some day cart so let me tell you about um rationalism versus empiricism so in the last video we looked at Knowledge from perception knowledge that requires experience of the world outside of our minds but there are potential sources of knowledge that don't require experience uh sources of knowledge that rely only on the resources we have within our minds and that's essentially what the rationalism versus empiricism topic is all about it's about the extent to which our knowledge comes from experience versus these other sources that rely only on the mind so broadly speaking the empiricist say all our knowledge comes from experience but the rationalists disagree the rationalists say there are other sources of knowledge such as innate knowledge knowledge we're born with and also that we can use intuition and dedu I.E the mind's capacities for reason to learn about the world so I've got to warn you this topic does contain a fair bit of philosophical jargon but uh once you get your head around the various Concepts involved I actually think it's one of the more interesting topics in epistemology so uh dust off your philosophy dictionaries and uh let's talk about rationalism versus empiricism [Music] [Applause] so the first thing to talk about with this topic is the definitions involved um the thing is uh a lot of these philosophers were talking about similar things before these definitions were even invented so they don't always neatly fall into one category or the other uh basically this rationalism versus empiricism topic is a bit of a mess so I'm going to editorialize the story a bit in order to avoid this video being 10 hours long so the first distinction we need to make is between a priori knowledge and a posteriori knowledge so this a priori a posterior distinction is about the different ways we come to know something a priorite knowledge is knowledge that can be gained without any experience of the world outside of our minds if you need help remembering this term the clue is kind of in the name a priori means prior to experience so examples of a priori knowledge include mathematical truths such as 2 + 2 = 4 for example uh you don't need to go out into the world and collect two stones and then then another two stones add them together count them and get four in order to know that 2 + 2 equal 4 you can work out 2 + 2 = 4 purely using your own mind so 2 + 2 = 4 can be known a priori then the opposite of a priori knowledge is a posteriori knowledge and this is knowledge that does require experience knowledge that can't be gained without experience or perception of the world out side of our minds and so again the clue is kind of in the name a posterior ey knowledge is knowledge that is acquired post experience or after experience so examples of aposteriori knowledge may include something like water boils at 100° Centigrade that's not something you can work out purely by thinking you'd have to do perhaps a science experiment to verify it likewise um today is a sunny day there's no way you could work that out purely by thinking purely using your own mind and so today is a sunny day is also an example of something that can only be known a posterior ey so the two sides of this debate disagree about how much of our knowledge is a priori and how much of our knowledge is a posteriori so broadly speaking the empiricists say all our knowledge is a posterior and there's no such thing as purely a priorite knowledge um this is a little bit of an oversimplification but we'll get on to that so empiricists say all our knowledge is a posterior and requires experience whereas the rationalists argue that uh we can use a priori sources of knowledge to learn about the world so broadly speaking there are two ways the rationalists argue that we can use a priori methods to acquire knowledge the first way is in knowledge knowledge you're born with and obviously when you've just been born you haven't had any experience yet so any innate knowledge would of course be a priority so the other way the rationalists uh argue that we can acquire knowledge a priori is via what's known as intuition and deduction so we'll get more into intuition and deduction later in the video but basically intuition and deduction are just the use of the mind's reasoning and logic capacities to firstly see that certain propositions must be true and then using logical deductions to derive further true propositions from what's already known purely using the mind and reasoning so intuition and deduction and innate knowledge are two ways that rationalism can reject the empiricist claim that all our knowledge comes from experience so we're going to start by looking at the innate knowledge debate so innate knowledge is knowledge you're born with knowledge that's perhaps encoded in your Gene somehow or preloaded into your mind and obviously when you've just been born you haven't had any experience yet so if innate knowledge exists then that is one way we can argue that we have purely a priori knowledge and thus reject the empiricist claim that all knowledge is a posterior right one extra thing to uh point out quickly here when we're talking about innate knowledge here we're talking about innate propositional knowledge specifically so if you remember from the definitions of knowledge video a few videos back we distinguish between ability knowledge acquaintance knowledge and propositional knowledge knowledge of facts and it's obviously uncontroversial that babies are born with some innate ability knowledge such as the ability to breathe otherwise they just die uh right off the bat so the rationalist claim about innate knowledge is that we have innate propositional knowledge so Plato the ancient Greek philosopher is someone who could definitely be characterized as a rationalist because Plato believed in innate knowledge Plato believed that before we're born into this physical world we existed in a different kind of almost alternate Dimension the world of the forms and the world of the forms is basically this world of Ideal perfect objects but we don't need to worry too much about Plato's theory of forms for this video but basically Plato believes that when we exist in the world of the forms we have perfect knowledge and when we're born into our physical bodies we we forget this knowledge and so all that we call learning within this life isn't actually learning it's just remembering stuff that we already knew in the world of the forms and so according to Plato all knowledge is effectively innate knowledge it just needs to be remembered Plato tries to prove his claim that all knowledge is just remembering in the dialogue meno and he attempts to show this by demonstrating how a slave who's never been taught geometry has knowledge of the geometric principle that a square with an area of 2 a will have sides equal to the diagonal of a square with an area of 1 a so so draws a square on the ground and divides it into four smaller squares just by asking questions and without telling the slave the answers the slave agrees that this square has an area of four and sides each with a length of two so Socrates then asks the slave if we were to double the area of this Square I.E if we had a square with an area of eight what would the length of the sides Be the slave initially answers four double the area double the sides right but Socrates draws this 4x4 Square on the ground and the slave realizes that if the sides are four in length then the area will be 16 and not8 the area has been quadrupled rather than doubled so the slave realizes that the length of the sides must be somewhere in between two the original square and four the square with an area of 16 so they try a 3X3 square but that doesn't work either because the area of a 3X3 Square will be 9 rather than 8 eventually sockes draws a square like the original 2x2 square but then draws diagonal lines across each of the four squares dividing them into eight triangles of equal size if you look at this diagram you could say there's a sort of smaller Square in the middle of the bigger Square that's composed of these four middle triangles and this smaller square has an area of four if you look it's made up of four triangles then if you look at the bigger Square you can see that it is composed of eight triangles it has an area of eight so this is the point the sides of the square with an area of eight were equal to the diagonal line of the original square with an area of four and the general principle here is that a square with an area of 2 a will have sides equal to the diagonal of a square with an area of 1 a and so Plato argues that the slave knows this geometry proof he knows this geometry proof and can answer the questions correctly without being taught geometry so Plato takes this to show that the slave's knowledge of this geometric proof is innate this isn't a geometry lesson it's philosophy so just to emphasize the philosophical Point here the philosophical point is that the slave has never been taught geometry he has no experience of geometry and yet he seems to know this geometric proof or at least can correct his mistakes when he makes them so Plato takes this to show that the slave's knowledge of geometry must be innate however there's lots of ways the empiricist could potentially reject Plato's conclusion that the slave boy knowledge here is innate for example You could argue that the slave was simply using reason to work out the correct answer after all it's not like he gave the correct answer right off the bat he initially gives a bunch of wrong answers before arriving at the correct one so perhaps he's just working out the answer as he goes or perhaps you could argue that asking questions as Socrates does to the slave boy is itself a form of teaching or perhaps some combination of both these explanations the slave boy bit in menow is not particularly long so uh perhaps it's worth reading for your yourself and deciding whether you think the slaves knowledge here really is innate or whether uh Socrates is basically forcing the poor slave to say the right answer perhaps a stronger argument for uh inate knowledge is liet's argument from necessary truths that knowledge of necessary truths is innate so I'm sorry to throw yet another definition at you but we have to make this distinction between a necessary truth and a contingent truth so firstly a contingent truth is something that is true but that might not have been true or that doesn't have to be true so for example um Paris is the capital of France is a contingent truth because while it is true it could have been false if whoever decided to make Paris the capital had decided to make uh Marse or leyon the capital instead likewise even something like uh the sun rises in East is a contingent truth because if the laws of physics had been different the sun might rise in the west or at some point before the earth existed the sun didn't rise in the east because the sun didn't rise at all so something like the sun rises in the East is also a contingent truth because while true it might not be true or yeah it might not have been true in contrast necessary truths are truths that are true have always been true and couldn't possibly be false so an example of a necessary truth that liit gives a few times is that it's impossible for the same thing to both be and not be simultaneously which is known as the principle of non-contradiction um mathematical truths are also typically understood to be necessary truth so 2 + 2 = 4 for example it just wouldn't make sense that in any Universe 2 + 2 could give you anything other than four so this is the argument we know that 2 + 2 = 4 is not just true it's necessarily true but how do we know it's necessarily true if I get these two onions and these two sweet potatoes and I add them together and I get four vegetables experience can only tell tell me that I got four in this particular particular instance but if all I had was my experience how would I know that you know the next time I add two things to two things I wouldn't get a different number well you know that's never going to happen you could add two things to two things from now until the end of time and you would always get four or even if I was transported to another dimension where time runs backwards and Aliens walk on the ceiling I would still still know that 2 + 2 equal 4 because 2 + 2 uh is necessarily equals 4 what are you talking about man so the point Li's point is that experience can only tell us what is true in this particular instance or that particular instance what's contingently true and yet we know that certain propositions such as 2 + 2 = 4 and noncontradiction are necessarily true so Lix argues that our knowledge that necessarily true necessary truths are necessarily true must be innate Li's uh new essays on human understanding where the necessary truths argument we just talked about comes from was actually written in response to John Lock's essay concerning human understanding and these two guys were a cont Temporaries they met each other and they met to discuss these and other topics so whereas liit thinks the Mind At Birth contained innate knowledge of necessary truths Lo's view is basically the complete opposite Loch argued that the Mind At Birth is a a tabular Raza which is Latin for blank slate in other words Lo believ that the Mind At Birth contained no knowledge and instead all our knowledge must ultimately come from experience so lot gives a hypothesis if you will about how all knowledge is built up from experience so lock First Lock distinguishes between two different types of experience sensation which is basically sense perception and reflection which is experience of thought basically experience of the operations of the mind so sensation can give us simple ideas such as blue or Square so for lock simple ideas are ideas that can't be broken down into anything simpler imagine a baby looking at the sky on a clear day for example this experience of sensation may give the baby the simple idea of blue but more complex experiences more complex Sensations can also give us complex ideas which are basically just combinations of these various simple ideas for example the baby May develop the complex idea of the Sea by combining the simpler ideas of blue and cold and water and wet and so on so complex ideas also come from experience but experience doesn't just include passively receiving Sensations like this our experience can also include the active combination of these ideas within the mind so for example even though a person may never have had experience of a unicorn for example because unicorns don't exist the idea of a unicorn ultimately is grounded in experience because it's formed from simpler Concepts that do come from experience such as white horse and Horn so in Lock's view all knowledge can ultimately be broken down into experience this way complex ideas are composed of simple ideas but all ideas are ultimately grounded in experience and so if we can account for all knowledge via experience via sensation and reflection then lot could argue that we don't need innate knowledge given that um all knowledge can be explained via experience there's no room left for the innate knowledge hypothesis innate knowledge is redundant in other words lock also attacks a different argument in favor of innate knowledge that because certain truths are agreed on by everybody then they must be innate firstly lock argues even if it were true that there were these propositions that everybody agreed on that wouldn't prove they were innate because that knowledge could be explained in other ways using experience such as the story of simple and complex ideas we just went over but what's worse says lock is that there aren't even any examples of propositions that really are universally agreed on we saw how libnet argued that knowledge of necessary truths such as 2+ 2al 4 and non-contradiction must be innate but Lo argues that children and idiots and that's a direct quote by the way Lo argues that children and idiots don't appear to know these truths if you look at a newborn baby for example there's no reason to suspect that the baby knows that 2+ 2 equals four or that it's impossible for the same thing to be and not to be simultaneously there's no reason to suspect that the baby knows anything so Lo rejects this idea that because certain propositions are agreed on by everybody that that's innate knowledge because there are no such propositions that are agreed on by everybody so live nits isn't happy to let lock have the last word here and the uh back and forth between liit and lock could justify its own video but what a lot of their disagreement comes down to comes down to sort of different definitions of what would count as innate knowledge so for lock something can't be innate knowledge if it's not something you've ever been consciously aware of but liit is sort of operating on a different understanding of what innate knowledge would look like liit says innate knowledge doesn't have to be conscious it's not like a baby comes out the womb right off the bat knowing that 2+ 2 equals 4 and that it's impossible for the same thing to be and not to be simultaneously however liet says the baby and all Minds have an innate predisposition to understanding these necessary truths so where lock describes the Mind At Birth as a tabular Razer liit describes the Mind At Birth as more like a block of marble I don't know what your knowledge of stonemasonry is like but take it from liit that a block of marble has a of veins running through it and these veins give the marble a tendency to take a particular shape when struck by a sculpter so according to livits uh our minds at Birth are similar to The Marble in the same way that the marble has a tendency to take a particular shape when struck by the sculpture the mind has an innate tendency to understand necessary truths when exposed to experience and and this tendency exists within the Mind At Birth and maybe liess has a point here um obviously babies don't come straight out of the womb saying it's impossible for the same thing to be and not to be simultaneously but as soon as they acquire language they seem to innately grasp the principle of non-contradiction so for example if you say to a toddler that it's your birthday to today but it's not your birthday today they're going to have a confused expression on their face because they innately know that that doesn't make sense that those two things contradict each other or once a a child's old enough to have learned its own name try telling it that their name is something different and they'll innately know to disagree with you because they innately grasp that if their name is Christian for example it's not possible for their name to be James because that would be a contradiction just to be clear here uh liin isn't saying we're born with innate knowledge of these specific examples such as knowing what day your birthday is or knowing what your name is but liit is saying we are born with innate predisposition towards the principle of non-contradiction and other necessary truths and that once we have experience we're able to apply these innate principles to the specific examples such as the ones just given so to summarize the innate knowledge debate Lo the empiricist argues that all our knowledge ultimately comes from experience and then the inates philosophers such as Plato and livits disagree so Plato argues that all our knowledge is ultimately innate and just needs to be remembered which is maybe a bit of a tough claim to defend but livess doesn't go quite that far liit argues that our knowledge of necessary truths must be innate because experience can only tell us what is true what's contingently true not what must be true such as necessary truths an important point to emphasize though is that both Plato and liet would admit that it does take some degree of experience to reveal the innate knowledge and this last point that it takes experience to reveal innate knowledge makes the innate knowledge debate a tough one to call because how do you know whether the experience is teaching the knowledge as lock would claim or whether the experience is just revealing the innate knowledge as uh Plato and liveness will claim so so that's the innate knowledge debate done but the rationalists still have another approach through which they can attack empiricism and that's intuition and deduction so I know I said earlier that empiricists say all knowledge comes from experience that all knowledge is a posterior ey but that was a bit of an oversimplification you see even the empiricists would accept that there are certain propositions that can be known entirely a priori such as uh mathematical propositions for example like the stones example earlier you don't need to do an experiment to know that 2 + 2 equals 4 it's something you can work out purely using your mind even the empiricist would agree with this so this is where I throw another definition at you and that is the distinction between an analytic proposition and a synthetic proposition so analytic propositions are propositions that are true in virtue of what the words mean True by definition so mathematical propositions are examples of analytic propositions such as uh 2 + 2 = 4 that's just what the words mean um another example of an analytic proposition would be something like all triangles have three sides because that's just what the word triangle means three-sided shape and and then the classic example of an analytic truth that's always used in philosophy is that all Bachelors are unmarried again that's just what the word Bachelor means it's an unmarried man and so um the concept Bachelor already contains the word unmarried and so all Bachelors are unmarried is an example of an analytic truth it's true by definition and so even both the rationalist and the empiricists would agree that we can know analytic truths uh a priori you don't need to do an experiment and Survey all the bachelors in the world to know that all Bachelors are unmarried so where the rationalists disagree with the empiricists is on the status of synthetic truths so synthetic truths are still true but they're true in virtue of how the world is rather than what the words mean so for example grass is green is a synthetic truth because um it's not like a bachelor you look I don't want I I just want to avoid saying Humes fork okay but basically you can imagine a red grass or a blue grass but you can't imagine a married Bachelor or a four-sided triangle so now I understand why this analytic synthetic distinction is a bit controversial as I try to explain it anyway ding ding ding ding ding ding water boils at 100° centigrade is an example of a synthetic truth because you couldn't work that out purely by examining the concept of water you'd have to do an experiment or something likewise uh frogs exist is an example of a synthetic truth Mount Everest is the tallest mountain in the world is another example of a synthetic truth again it's not true by definition in theory you could find another Mountain that's even taller or octopus is have three hearts and blue blood is another example of a synthetic truth because just by knowing what an octopus is what the concept means you can't learn that it has three hearts and blue BL in general most synthetic truths can only be verified a posterior ey after some sort of experience or observation so returning to the examples a couple of seconds ago uh frogs exist could only be verified a posteriori you couldn't work out that frogs exist purely by thinking or locked within a you know a cell with no access to the outside world unless a frog came into your cell but getting bugged down in the example again you're locked in a Cell no contact with the outside world you can't work out a priori that frogs exist or that Mount Everest is the tallest mountain on earth or that water boil is at 100° C you can't work those things out a priori and so most synthetic truths can only be verified a posterior right the question at least of the intuition and deduction topic is whether this relationship holds true all the time or whether there are exceptions and so the rationalists claim that there are exceptions that there are some synthetic truths that can be learned purely a priori using intuition and deduction now in plain English this is like saying that we can use the mind and thinking to learn about the world outside of our minds so dayut the great dayart uh is another philosopher who could be characterized as a rationalist not so much for his belief in innate knowledge but more through his use of intuition and deduction to learn about the world so at the start of meditations deart wants to work out what he can know he wants his knowledge to be built from the ground up from firm foundations and so to do this he starts by doubting everything that's possible to doubt by the end of the first meditation dayart is doubting all his perceptions and experiences in other words he's doubting all a posterior knowledge and actually he's goes even further than that but we'll talk about that more in the next video anyway dayart doubts the evidence of his senses of his perceptions because it's possible that all those experiences and perceptions were just Illusions or lies put there by an extremely powerful evil demon that's deceiving him if you think about how you can sometimes be dreaming and not realize it or films like the Matrix where your entire life is a lie and you don't realize it that's kind of the point dayar is getting at here it's it's possible that everything you've ever seen or heard is a lie and so you can't trust it as a source of knowledge it's possible to doubt and so the point at least as far as this rationalism versus empiricism debate is concerned is that dayart has ruled out any aposteriori sources of knowledge and so from this Foundation of extreme doubt all dayart has is a priori methods through which he can rebuild his knowledge in other words he has to use his intuition and deduction just the powers of his mind to get himself out of this skeptical Quagmire the phrase Kito ero Latin for I think therefore I am is probably the single most famous bit of philosophy ever so what does it mean well I mentioned earlier how at the end of the first meditation deart is doubting pretty much all his knowledge because it's possible that he could be being deceived by an extremely powerful evil demon however and this is the point of the Kito argument even if that is the case even if darar is being deceived by an evil demon and everything he's ever seen or heard has been a lie he can't doubt he exists because there has to be something that's being deceived by the evil demon in the first place the full phrase of the Kito argument is uh dubo ero Kito ero Sam which translates to I doubt therefore I think therefore I am for dayar the Kito argument is an example of a a rational intuition it's not something that's learned bya experience and it's not even a deduction instead says Daya and this is a direct quote I am I exist is necessarily true every time I express it or conceive it in my mind so a priorite intuition rational intuition as dayart says is kind of the ability of the mind to see that certain proposition are true just by thinking about them and this is important in the rationalism versus empiricism debate because remember empiricism says that a priori methods such as intuition and deduction can only tell us analytic truths but here with the Kito argument deart has established the synthetic truth I am or I exist using only a priori intuition and deduction so if this argument works and is entirely a priori then dayart has proved rationalism is correct and empiricism is false so you can think of the previous Kito argument as the sort of springboard from which dear is attempting to rebuild his knowledge but obviously I exist isn't much knowledge and at this stage in the med meditations all a posterior knowledge is still off limits they still can't trust his perceptions and his experience so from this platform deart continues working within the a priorite limits of his own mind to try and establish further synthetic truths Beyond simply I exist the Kito argument was an example of a rational intuition but the other tool dayart has the other a priori method deart use can use to learn about the world is uh logical deduction so logical deduction is the use of reasoning to derive true propositions using logical necessity from what is already known so for example if I were to allow you that all cats are mammals and that Dave is a cat then using logical necessity you could deduce that Dave is a mammal because Dave is a mammal logically follows is logically guaranteed by the previous two uh premises so the next synthetic truth deart seeks to establish using only these a priori tools of intuition and deduction is that God exists so deart gives a fair few Arguments for God's existence in meditations but we'll cover most of them when we get onto the metaphysics of God topic instead today we're only going to focus on dayart so called trademark argument for the existence of God so the trademark argument goes something a bit like this firstly I have the idea of God within my mind that's the starting point and the idea of God is the idea of an infinite and perfect being says dayar then the next premise is what's known as the causal adequacy principle dayart says that the cause of an effect must have as much reality as the effect so if that makes no sense whatsoever perhaps picture getting punched by a ghost would that leave a physical Mark presumably not because the physical Mark such as a bruise would have more reality than the cause I.E The Ghost and so the cause of the bruise would have less reality than the effect and dayut says that's not how things work so applying this causal adequacy principle to the idea of God that dayart has in his mind dayart says that the cause of this idea of God must have as an infinite and perfect being must have as much reality as an infinite and perfect being and so an infinite and perfect being must exist and so God exists the trade Mark argument is called the trademark argument because dayart seems to think of the idea of God as like a trademark that God sort of stamps in everybody's mind and because of the causal adequacy principle Dart says that this trademark could only have been put there by God himself and so with the trademark argument dayart has potentially established yet another synthetic truth that God exists using only the a priorize sources of intuition and deduction and dayart doesn't stop there having established that I exist the Kito argument and that God exists the trademark argument dayart seeks to establish a third synthetic truth using only the a priorize sources of intuition and deduction the synthetic truth that the external world and that mind independent objects exist so deart says he seems to perceive mind independent objects as sort of physical substances that's his starting point and so his next step is to question the cause of these perceptions of physical objects so dart rules out his own mind as the cause of his perceptions of these physical objects because if it was his own mind that was causing these perceptions then he'd be able to control what he perceived decart's argument here is very similar to uh Lock's argument from the involuntary nature of perception that we looked at in the previous uh Knowledge from perception video so if decart's perceptions of physical objects aren't caused by himself deot says the other two possibilities are objects themselves or God god well God exists but if God was the cause of my perceptions then that would be a bit misleading because my perceptions seem to tell me that when I'm looking at a physical object the object really exists outside my mind and if it was just a an image or a perception put there by God and the object didn't really exist then that' be kind of a bit deceptive and God as an infinite and perfect being doesn't do that God wouldn't deceive me like that so that only leaves the cause of the perception of objects as the objects themselves in other words dayart says that the cause of his perceptions of physical objects are physical objects themselves and so physical objects and the external World exists so there you go the external World exists the third synthetic truth that dayart has Prov approved purely using a priori intuition and deduction or has he perhaps as we were going through day cart's three arguments using intuition and deduction just now you sense a few cheap moves along the way you sense that a few premises in decart's arguments here were not entirely a priori but perhaps a posteriori and that's certainly what the imper would argue the empiricist would argue that even if decart's conclusions are true and his arguments are sound the arguments are not entirely a priori there are instead aposteriori premises that could only be known with some degree of experience one such empiricist is David Hume and hume's Fork not Fork as in knife and fork but fork in the road distinguishes between two types of proposition relations of ideas and matters of fact I don't want to get bogged down in yet another set of definitions especially since hume's Fork overlaps so closely with the a priori a posteriori and analytic synthetic distinctions we've already made so instead I'm going to frame hum's Fork as a kind of test we can do to test whether a proposition can be known a priori or whether it can only be known known a posterior right can you imagine the proposition being false if not then the proposition is what hum call a relation of ideas and it can be known entirely a priorite but if the proposition we can imagine being false then it's not a relation of ideas say assume it's a matter of fact and it can only be known a posterior right so let's apply this test to a few propositions for example we can know triangles have three sides a priori because we can't conceive of it being false if you try and imagine a four-sided triangle for example do it now what are you imagining either you're imagining a four-sided shape in which case you're imagining a square or you're imagining a triangle but the idea of a four-sided triangle is not an image you can bring to your mind and so triangles have three sides would be a relation of ideas according to Hume and something that can be known entirely a priorite in contrast if we apply the Humes Fork test to the proposition grass is green it reveals it to be a matter of fact rather than a relation of ideas because we can conceive this proposition being false for example we could imagine blue grass or red grass these ideas make perfect sense they are conceivable and so grass is green is a matter of fact and can only be known a posterior right according to Hume so if we apply this test Humes Fork to decart's arguments we looked at a minute ago do we find any premises that we could conceive of as being false if so this would suggest that these arguments are not entirely a priorite as dayart claims so working backwards I can think of at least one premise in decart's argument for the existence of the external world and substance and mind independent objects that is conceivably false and so fails hume's Fork at least as a relation of ideas so the premise I'm thinking of if you remember is uh when dayart says his perceptions must be caused by something outside his mind because his perceptions are involuntary but if we think about that premise is it conceivable that it could be false is it conceivable that you could have perceptions that are involuntary but are nevertheless caused by your own mind well yes uh Dreams Are One such example so when you're dreaming unless you can lucid dream what happens is outside of your control it's involuntary and so this shows that it's perfectly conceivable ordinary even for perceptions to be caused entirely by your own mind and yet be involuntary so hum would say you cannot know a priori that your perceptions aren't caused entirely by your own mind even if it is ultimately true that your perceptions are caused by mind independent objects and so day Cut's conclusion here is true Humes Fork shows that the reasoning is not entirely a priori because it's conceivable that it could be false what's more decart's argument for the existence of the external world and mind independent objects relies on his previous argument that God exists and so if we can show that the trademark argument for example relies on a posteriori matters of fact then this further weakens the case that day cart's argument for the existence of the external world is a synthetic truth proven only via a priorite intuition and deduction Humes for can also be used to argue that various premises in decart's trademark argument for the existence of God also rely on a posterior matters of fact for example the causal adequacy principle decart's premise that the cause of an effect must have as much reality as the effect applying Humes Fork to the causal adequacy principle raises the question of whether it's conceivable that we could imagine a cause with less reality than the effect to conceive of a human being creating the idea of God is not a contradiction like a four-sided triangle the idea makes sense we can imagine perfectly coherently that a finite and imperfect human being could somehow create the idea of an infinite and perfect being that's a coherent idea and so dayart would say this is a exception to the not dayart what am I saying and so these examples show that the causal adequacy principle even if it's true it can't be known purely a priori because we can conceive of it being false we need to do some uh investigation or observation of the real world in order to know that the cause and effect does indeed have as much reality as the effect what's for going back to the innate knowledge debate a minute ago we can question where the concept of God in decart's mind comes from whether this concept is entirely a priority so dayart claims the concept of God is stamped in his mind like a trademark from birth so deut would claim the concept of God is innate but we could use locks tabaza arguments and apply them to dart's claim that the concept of God is innate so again children and idiots do they have the concept of God if you look at a newborn baby is there any evidence to suggests that the baby has the concept of God if not perhaps the concept of God rather than being a trademark that's stamped in our minds from birth as dayart claims perhaps the concept comes from experience as Lo points out there are entire atheist cultures of adults who lack the concept of God and so this further weakens the claim that the concept of God is a priority and so if the concept of God requires experience then this is further reason to argue that decart's trademark argument fails to establish the synthetic truth God exists purely using a priori means finally the kago argument I exist now this argument withstood even the evil demon scenario so surely this most certain of propositions can withstand hume's empiricist Fork well the Kito argument is probably the strongest candidate for synthetic a priori knowledge but Humes Fork takes this on too so hum argues that all we ever experience is a bundle of perceptions we experience constantly changing thoughts and Sensations but we never actually experienc a self in other words we never experience the thinker of the thoughts only the thoughts themselves and so the jump that dayart makes from I think to I am or I exist doesn't necessarily follow at least it doesn't follow a priori it's a strange idea to imagine but we can at least conceive of a thought without a thinker and so all thoughts have thinkers if it's true it's true as a matter of fact rather than a relation of ideas perhaps we could imagine the evil demon is just creating a bunch of disembodied thoughts that I exist this is a conceivable idea it's not like a four-sided triangle or a married Bachelor and so again even if all thoughts have thinkers is true and so day carts jump from I think to I am is is uh sound hum would argue that at most the Kito argument proves that thoughts exist a priori but that it requires some a posterior reasoning to jump from the thoughts to a thing that exists and is thinking these thoughts so to sum up the intuition and deduction debate the rationalists say we can use a priori intuition and deduction to establish knowledge of synthetic truths now in plain English this is like saying that we can use the mind and thinking to learn about the world outside of our minds but the empiricists disagree so we saw how dayart the rationalist attempts to provide proofs of three synthetic truths I exist God exists and the external World exists using only a priori intuition and deduction but we saw how Humes Fork challenges whether these ARG really are entirely a priori or whether some of the premises rely on a posteriori experience however like I mentioned at the start of this video this uh debate is a little bit artificial because a lot of the terms such as rationalism empiricism analytic and synthetic didn't even exist when a lot of these philosophers were writing for example dayart had been dead for over a hundred years when K invented the analytic and synthetic distinction so it's a bit of a stretch to say that dayart was trying to prove synthetic truths using a priori intuition and deduction when dayart wouldn't have even had the concept of a synthetic truth similarly dayart died long before Hume came along and so we can only speculate how dayart might defend or not the kago argument against Humes Fork the reality is most of the philosophers we've talked about today don't fall perfectly into either rationalists or empiricists and indeed the understandings of these very terms rationalism and empiricism aren't very clearly defined and have changed a lot over the years that said I still think this is an interesting topic because um it gets us thinking about where our knowledge comes from how we just ify it and how certain we can be of it which is the topic of the next video congratulations on making it to the end of another one of my uh dumb philosophy videos but I hope you enjoyed it um now it's time for uh my favorite part of these videos which is the bit where I review the book so as always you can get my book um obviously that one gets a a thumbs up from me um it basically goes over the same stuff we went through today the rationalism versus empiricism topic broken down into the innate knowledge stuff and the intuition and deduction stuff then as far as uh primary sources we got a lot to get through today um once again we've got Lock's essay concerning human understanding I know I ripped on it in the last video but it is really boring and long so um I don't know but just to prove I'm not biased against empiricist David Humes inquiry concerning human understanding gets a thumbs up from me I like this book um not just because it's shorter but because uh it's just more interesting then uh to complete the trilogy of human understanding we've got liet's new essays on human understanding now for a guy who had such a kind of flamboyant wig his writing style is uh surprisingly clear and uh I really like this book actually so that one definitely gets a thumbs up from me surprise and then uh Plato's menow um I always recommend people's uh people Plato's dialogues but I've hardly read any of them myself but they are quite readable I've read the uh slave boy bit of this book and yeah it's enjoyable so thumbs up for me and then uh got to get both thumbs up for this one day carts meditations now I know I always bang on about it but I really do like this book um it really is the it just this is what philosophy is all about so uh yeah love day Cuts meditations anyway I'm going a bit mad so it's probably best to uh close the video off there thank you so much as always for watching and yeah we will see you in the next one [Music]