Basic Logic, Propositions and Syllogisms (Aristotle's Logic)

what's up everyone my name is Richard and like to welcome you to my new YouTube channel in this video I want to teach you guys some basic logic first off what is logic exactly the 18th century English philosopher Isaac Watts defined logic in the following way he said logic is the art of using reason well in our inquiries after truth and the communication of that truth to others so why should we study logic we should study it because it will help us reason more effectively what sets up what sets humans apart from the animals is the fact that we have reason therefore we should train our rational faculties so that we don't get tricked by the faulty or deceptive reasoning of others so let's proceed what does the first word we need to learn in logic the first word is proposition what is a proposition I wrote it down for you I'll show you a proposition is any sentence that signifies either truth or falsehood a proposition is any sentence that signifies either truth or falsity there is a more technical definition used by philosophers and that definition is a proposition is the content or meaning of a declarative sentence capable of truth or falsity but we won't be using that one we'll stick with this easier one which was given by the 16th century English logician Thomas Wilson so is that fishing is still pretty good we'll be using this one so let me give you some examples of propositions the sentence I like pizza is a proposition that sentence can be true or false the sentence Isaac Newton was a scientist as a proposition because that sentence can be true or false it's important to note that commands cannot be propositions because they can't be true or false the statement do your homework cannot be a proposition because it can't be true or false commands can be obeyed or disobeyed but they cannot be said to be true or false likewise questions are not propositions if I ask you how are you that sentence itself can't be true or false your answer could be a proposition you could say I'm doing well and that can be true or false but um the question itself cannot so good first thing is proposition a proposition is any sentence that signifies either truth or false in the next two words we to learn are the words premise and conclusion so what's a premise a premise is a proposition that logically proves or supports a conclusion a premise is a proposition that logically proves or supports a conclusion what is a conclusion a conclusion is a proposition that logically follows from the premise a conclusion is a proposition that logically follows from the premise so an argument consists of a premise and a conclusion so let me give an example um Bob eats three greasy Big Macs per day therefore Bob is supremely overweight so in that argument the sentence Bob eats three greasy Big Macs per day is the premise the sentence therefore Bob is supremely overweight is the conclusion so on one follows from the other but technically the more complete formula the more complete form of an argument is what Aristotle calls a syllogism what is a syllogism a syllogism is this a syllogism consists of three propositions major premise minor premise and conclusion in this example all men are mortal this is a universal proposition the minor premise is Socrates is a men this is a particular proposition and the conclusion is what follows from the premises Socrates is mortal so all men are mortal Socrates is a man therefore Socrates is mortal what's beautiful about a syllogism is that if the first premise if the major if the major/minor premises are true then the conclusion will always follow provided that the form of the argument is valid see that's what's beautiful what logic if certain propositions are true there are other ones that are logic connected that must also be true and this could be put in mathematical form all a is B all C is a ball C is B ABC can indicate anything men mortals animals whatever so in our previous example all men are mortal Socrates is a man therefore Socrates is mortal when you're debating someone you have two options if you wish to refute their argument on the first option is to prove that one of the premises are false if you could show that one of these are contrary to reality than your opponent's argument Falls the second option is to show that the conclusion does not logically follow from the premises there are arguments in which the premises are true but the conclusion does not logically follow and when that happens you could use a fancy Latin phrase non sequitur non sequitur and this means it does not follow so if you want to sound smarter than you actually are use the phrase non separate or Latin is good for being pretentious very nice so a review of how to refute someone's argument you could either prove that one of the premises are false or you could prove that the conclusion does not logically follow from the premises and if you've done that you find the argument well you've destroyed your opponent's argument and you have to present your own now nice I'll leave it at that thanks for watching if you enjoyed this video press that like button subscribe and leave a comment my next video should be on next week so I'll see you then peace

Channel: Richard Min

Views: 50,407

Keywords:

Id: 1UmPbfuGfKk

Length: 5min 27sec (327 seconds)

Published: Sat Feb 03 2018