I can't believe how long these videos have been around now! I first used them ten or so years ago when I tried to go through Hurley's text on my own. Now I am taking a logic course, having returned to college at the ripe old age of 65!! I need all the help I can get, and these videos just clarify the more difficult sections perfectly. Thank you for these excellent lectures!
I tried so many online tools and tried to find tutors on critical thinking and filled to do well. These videos however have saved me! I am doing well after watching these and I actually understand the content!
You are officially my new philosophy teacher! I'm using a later version of the book you have. Mine is from 2019, but I'm taking online classes and we don't get live lectures or videos of the step-by-step processes! With your help, I will be able to get through this weeks work in Chapter 4 and 5. Thank you!!!
Thank you so very much for posting these videos, i find them extremely helpful in my online-phil. class. you put the visual to my course readings and help make the text much more simpler to understand! thanks!
This one is hard. I’m fine with understanding the A E I O, the quantified, and the copula. I even grasped the difference between Aristotle and Boole (the universal known and unknown.) My trouble started with the distribution thing. It means empty when you fill it up? I suppose I need to read the book and watch the video again. Thanks, Professor Thorsby.
Mark Thorsby...You don't know how great you are , bro. Thanx ! Please, do describe some of the symbolically written statements in the books as well and how to pronounce them..like ∀x(Sx → Px) & ∃xSx. and other such forms ..pleaseeeeeeeee.
I think you did very well. I was hoping to hear more on existential fallacy, since it is also in Hurley 4.3 section, nevertheless, I followed your diagrams and made a perfect tool. Thank you
But why Boole changed the meaning of "all" excluding existential import? And altering the more common and natural meaning of "all" in languages? (btw thanks for the interesting video :-))
Hi Cesco, that is a good question. The question ultimately is answered by Boole in terms of his commitment to an empirical epistemology and his view that logic is fundamentally negative. In his work, he set out to create an algebraic system for assessing logical arguments. We only gain knowledge of particulars over time. I know what what a horse looks like by seeing one horse, then, another, and over time generalizing that knowledge to extend to the entire category of horses. But there is no way in which I could ever verify that my information about horses will always extend universally. Of course, we do know that a particular thing exists, and so we can extend the assumption of existential import to particular propositions, but we can't assume the same thing for universals. Hence, if something exists particularly, we cannot infer the existence of the universal (illicit subalternation). I hope that helps. You can read Boole's work free on Google Books.
@@PhilosophicalTechne Hi Mark, thank you very much for your prompt answer. Yes, I have read dozens of articles on why modern logic changed the meaning of "all", but I havent found yet a convincing answer. I explain here my point of view, and I d like to see if it has errors and why. 1) The existence should be analysed in a context. If my context is the real world then "some cats fly" is false, but if my context is Wonderland it is true: in Wonderland some flying cats do exist. 2) First we have concepts, then words appear in languages (or are invented) from the need to express such concepts. 3) The definition of the meanings is and should be taken from the statistical use of the words (that's how words evolve and get new meanings) or from their definitions (when they are invented by someone). 4) The domain of quantification might be void if the defined word is not existent in the chosen context (e.g. if my context is Mars the proposition "some trees are green" is false, because on Mars there are no trees, and so the domain is void) 5) The word "tree" is defined as "plant with a stem, etc...". So if our context is Earth, "all trees are plants" is true by definition, we dont need to check every tree. And it has existential import, so it implies that some trees exist (on Earth), and we can easily verify that it is true. 6) The word "all" in the great majority of cases in natural languages and everyday logic has existential import, as it was in ancient logic. In some cases there is no existential import, but they are a minority of cases, such as laws; in laws there is an implicit conditional hypothesis: all thieves in the school should get arrested = if a thief is found in the school, s-he will get arrested. 6.1) And even in these cases we could argue that in the hypothetical context that we are analysing (thieves found in the school) the thieves exist by hypothesis. But I agree that this point is debatable. 7) So my question is: why Boole (and modern logic) decided to modify the well established prevalent meaning of the word "all"? If he needed to express concepts without existential import, the concept (and related statement) was already present in ancient and everyday logic: "No S are not P". He could have let "All S are P" keep its ancient and everyday common meaning with existential import. Why did he do this choice and why modern logic followed this path? I am sure there must be an extremely good reason but I am still looking for it ;-) Concerning horses: if I do the hypothesis that "all horses have a tail", (and the tail is not an element in the definition of horse) then I agree that I should check all horses, in this case the statement is simply undefined: neither true nor false, until when I will have checked all horses; there is no need to change the meaning of "all". But I could say "all horses in my ranch have a tail", and I know that it is true because I have only 3 horses in the ranch and they all have a tail, so in this case the sentence is true and has existential import. Again, no need to change the meaning of "all".
