A.J. Ayer, Language, Truth, and Logic | The Criterion of Verifiability | Philosophy Core Concept

hi this is dr. Gregory Sadler I'm a professor of philosophy and the president and founder of an educational consulting company called reason IO where we put philosophy into practice I've studied and taught philosophy for over 20 years and I find that many people run into difficulties reading classic philosophical texts sometimes it's the way things are said or how the text is structured but the concepts themselves are not always that complicated and that's where I come in to help students and lifelong learners I've been producing longer lecture videos and posting them to youtube many viewers say they find them useful what you're currently watching is part of a new series of shorter videos each of them focused on one core concept from an important philosophical text I hope you find it useful as well what a gar calls the criterion of verifiability is arguably the most central concept in his short work language truth and logic and he introduces it of course in Chapter 1 within the very first several pages after telling us how his project differs from that of other people he's going to lay out what this criterion is and make a few distinctions within it he'll also use those to distinguish himself against several other positivists logical positivists actually and set out L tamiya a reformulation of this principle in terms that are going to run throughout and be applied within the entire work including chapter 1 so what is the criterion verifiability he tells us that it says that a sentence is factually significant to any given person if and only if that person knows how to verify the proposition which it purports to express now that's a little bit of a strange formulation and there's a bit of technical jargon going on there so we want to unpack this before we move factually significant it has some sort of sense it's going to be able to be said to be true or false to any particular person right or a group of people and then the if and only if that's a biconditional it's very important it's defining what it means for a sentence or an expression or proposition to have that status then where he's going to talk about how to verify the proposition we'll get into that in just a moment and then notice the proposition which it purports to express that part you could actually leave off if you wanted to technically a sentence expresses a proposition this is some basic logic stuff there but we don't actually need to worry that much about this this particular issue we're more interested in this issue of what does it mean to verify and how to verify so what observations would lead us to taking a definitive stance on the truth or falsity of this proposition he says that if the person knows how to verify it right if they know what observations would lead them now notice this important provision under certain conditions to accept the proposition as being true or rejected as being false so there's a lot of things that we can say well you know I'm not sure whether this is true or false and that doesn't mean that they're therefore unverifiable or they're not factually significant as we're going to see we just have to know how we could actually go about verifying them if indeed we we can if a sentence doesn't fit that description then it's what he calls a tautology and he discusses that here or it's what he's gonna later call on the work strictly speaking nonsense and both tautologies and nonsense are pseudo propositions pseudo is actually not the best term to use the technically speaking it means lying or false right but as we're gonna see tautologies they're always true right and nonsense is neither true nor false so it's a little bit of a misnomer there but he says that if the proposition is of such a character that the assumption of its truth or falsehood is consistent with any assumption whatever concerning the nature of one's future experience then it is if not a tautology a mere pseudo proposition the sentence expressing it may be emotionally significant right but it's not factually significant so there's emotional significance and we get into that with the whole emotivist theory of ethics and you know perhaps in other parts of the work as well and then there's factual significance it actually says something about the world that we can observe and experience now a set of distinctions have to be made and these distinctions are made in part to respond to you might say knee-jerk responses that that a person could easily make to say well there's very little that's actually verifiable in this this definition so one of the key distinctions that he makes first is that between what he calls practical verifiability versus verifiability in principle there there are many things that we can't practically verify for example in the time that we're existing right now the video that you're watching might not actually be me dr. Sadler talking to you and it could be a deep fake as we call them now right and we're gonna have more and more of these as time goes on unless legislation to somehow pass to rule these out we now have the technical means to take words and feed them into rather sophisticated ai's that can then generate those words in the voice of somebody else and with the face of somebody else with the right facial expressions and it's just gonna get better and better and better better in the sense of getting more and more able to deceive us okay so how would you actually verify that this video was me talking to you well you'd have to be here in the room standing right next to me verifying for yourself that that was the case or perhaps there'd be some other electronic marker that would work as a proxy that we could use but that's that's that's practical verification that's not really what is feasible for anybody who's watching this now isn't instead what we have is verifiability in principle were you to be here counterfactually you would be able to observe that it is indeed me and not a robot not a dr. Sadler impersonator not the product of a deep fake that is giving this lecture on a Jair and for that matter how do we know that a Jair wrote this book how can we verify that for the guy's dead he actually lived quite a long life I know some stories I believe it or not about a gar that because he came to Southern Illinois University where I did my graduate studies and people said some rather interesting and colorful things about him how do I know that these anecdotes are actually true I could go back and you know ask the people but is that verifying no it's not practical verification but verification in principle I suppose were I to have been there I could do that and there's all sorts of things that we don't know at the present air uses an example that we actually can verify now whether there are mountains on the further side of the moon he says no rocket has yet been invented which would enable me to go and look at the farther side of the moon so I can't decide it by actual observation but I do know what observations would decide it for me yeah as is theoretically conceivable I were once in a position to make them I'll give you another example from something that's coming from our real life right now we have two aging pets both of whom have things you know going wrong with their organs in different ways and they can take MRIs and ultrasounds and interesting things like that and they can say well you know there appears to be this thing going on here but unless we do a biopsy we can't really be sure of what's happening but we're not going to do a biopsy because it would be incredibly invasive so we're just gonna say that this is the case that this is the case it is in principle verifiable if we wanted to do a biopsy which would be you know intrusive painful and probably expensive and most likely unnecessary but we're not going to do it and so it's only verifiable in principle and we could go on and on and on we can have all sorts of interesting hypotheticals about what a person would do I would give my life for you how do you verify that do you actually have to see the person give their life for you or can you imagine some circumstances in which that would be made true or made false so he gives do some interesting examples he gives you an example of a metaphysical pseudo proposition taken from Bradley the absolute enters into but is itself incapable of evolution and progress Ayer says this is not even in principle verifiable I have no idea what would allow you to determine anything about the absolute and whether it enters into evolution or progress he says I mean it's possible that these are code words and the person is using these English terms in a rather non-standard way but in that case it has to be translated into a more ordinary approach to language so we could in fact verify it so that's the distinction between practical verifiability and verifiability and principle very important one to observe another very important distinction is between what air is going to call strong and weak senses of verification he says a proposition is said to be verifiable in the strong sense of the term if and only if it's truth could be conclusively established and experienced but now he's telling us about the other side it is verifiable in the weak sense if it's possible for experience to render it probable so he says that why do we need to make this distinction well some positivists want to adopt conclusive verifiability as the criterion of significance and he says that's gonna run us into some problems if we think about general propositions of law and here he doesn't mean legal systems he means things like natural law so for example arsenic is poisonous all men are mortal a body tends to expand when it's heated he says it's of the very nature of these propositions or truth cannot be established with certainty by any finite series of observations why because there could always be some sort of exception and you can't actually observe every possible case of these so you're making an assumption that you know what we observe in the future is going to be similar to what we've observed in the past and in the present and that nature has certain regularities to it once we've observed enough of it so according to the strong conception of verification those natural laws or you know whatever we want to call them generalizations is probably better than laws any one of them would not be verifiable and then we'd have some real problems right we wouldn't be able to do science instead air proposes that we can rely on probability so he says that here we go he thinks that no proposition other than a tautology can possibly be anything more than a probable hypothesis and he says if this is correct the principle that a sentence can be factually significant only if it expresses what is conclusively verifiable would be self stall to fiying that is it would be making one stupid literally it has a criterion of significance so you know that's a key thing he also says we also cannot accept the suggestion that a sentence should be allowed to be factually significant if and only if it expresses something which is definitely confute about by experience confute abomey pnes it can be refuted it can be shown to be wrong it can be shown to be false so he says those who adopt this course assume that although no finite series of observations is ever sufficient to establish the truth of hypothesis there are crucial cases in which a single observation can definitely confute it he thinks that that's not the case either so we have to rely on probabilities so error is proposing this this entire criterion in terms of verify ability and principle and a weaker sense of verifiability that can be based on induction so he ends up coming to another formulation of this he says let's make our position clear let us call a proposition which records an actual or possible observation an experiential proposition then we can say that it is the mark of a genuine factual proposition not that it should be equivalent to an experiential proposition or any finite number of experiential propositions but so here's the criterion now simply that some experiential propositions can be deduced from it in conjunction with certain other premises without being deducible from those other premises alone now why bring in this extra stuff about these other premises and not from these other premises alone because generally in order to get something off the ground we actually need a whole set of proposition some of which may not be empirical some of which are not being brought into question here but we should be able to deduce not just induced but deduce he says some experiential proposition from whatever it is that we want to take as being factually significance that that is as having a meaning as something that can be said to be true or false and not in the sense of a tautology which is always true rather we want to be able to say what we could verify from this that's this proposition so this is another way of formulating it this is going to be a absolutely central idea running throughout the entire text and you could say heirs approach in general you

Channel: Gregory B. Sadler

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Keywords: Lecture, Lesson, Talk, Education, Sadler, Philosophy, Learning, Reason

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Length: 16min 5sec (965 seconds)

Published: Thu Nov 21 2019