-Back in Antiquity, "logic" was considered to be a "tool" or "instrument" for philosophy, but not an actual part of philosophy itself.
-Aristotle's works on logic are referred to as "The Organon" ("The Tool" or "The Instrument").
-Includes 6 works:
-"Categories"
-"On Interpretation"
-"Prior Analytics"
-"Posterior Analytics"
-"Topics"
-"Sophistical Refutations"
-Additionally, there are two other surviving works that we have (but are not included in the Organon, although they do involve logic)- "The Rhetoric" and "The Poetics".
-"Prior Analytics" is the only one that deals with logic in terms of how we would understand it today.
-It analyzes the forms of logic separate from their content. For example, "If every A=B and every B=C, then every A=C."
-"Categories"- comes from the Greek word "katēgoria" ("blame", "statement", or "accusation"), but Aristotle uses it to mean "predication" (i.e. saying one thing about another thing).
-Makes points about words that are predicated (e.g. difference between synonyms and homonyms).
-Also makes a distinction between what is an essential feature of something and what is accidental. A feature or predicate is essential if it has to do with the nature of the thing being discussed. For example, it is essential for a giraffe to be a) a giraffe, b) an animal, c) have other features required for membership in the giraffe species. However, if the giraffe is painted blue, this is characteristic that is "accidental" or "present" in it. It is also "accidental" if it happens to be sick, especially strong, etc.
-Therefore, if you can change a feature of something without "destroying" the whole thing, then that feature is "accidental".
-The work goers on to provide a list of "categories" (i.e. types of things that can be predicated): substance, quality, quantity, relative, place, time, position, state, action, and being acted upon.
-It's possible that this is not something new that Aristotle came up with on his own, and is entirely likely that he learned a lot of this stuff at the Academy under Plato.
-"On Interpretation"- focuses more on the philosophy of language.
-Plato explored this in his dialogue "Cratylus" (the theme: do words have significance by nature or convenience?).
-Aristotle states immediately that words have meaning by conversation, not nature. However, not only are words symbols of meaning (but are not the meaning in and of themselves), but they also represent a thought in one's own soul.
-In fact, there is a CHAIN of representations! If you write down a word, that word represents the spoken word, which represents the thought in your soul. Therefore, verbal language is more "fundamental" than written languages. Additionally, the thought in your soul represents whatever thing in the world you are trying to express.
-However, the main focus of the work is the study of sentences that assert or deny something.
-Also makes the distinction that some predications are universal, where others are particular. Aristotle uses this concept to explore which sentences are opposed to which.
-A statement is contradictory to another if it is an exact negation of it.
-This can be confusing. For example, the contradictory statement to "All humans are white" is NOT "All humans are not white", but instead "Some humans are not white." This is important because for every pair of contradictions, one (and ONLY one) can be true. For example, either there is at least one non-white human, OR all humans are white. It can't be both; it has to be one or the other.
-Aristotle then says that with any pair of contradictory statements, one will be true and the other will be false.
-The only problem is- what if we're discussing the future? If you make a statement about the future and it is indeed true, does that mean that the future is already decided and that everything that happens has happened regardless of any choices we make?
-Aristotle's solution to this troubling idea is that any statements about the future are neither true nor false, so with this he makes an exception to his rule about contradictions.
-Unfortunately, this isn't a satisfying answer for the reader because what happens when someone accurately predicts the future? Obviously, this creates some headaches.
-"Prior Analytics"- contains information on "logic" in terms of how we would describe it today.
-Discusses sentences put together into arguments.
-In this work Aristotle introduces the concept of the syllogism ("syllogismos").
-For example, "All mammals are animals. Some mammals are giraffes. Therefore, some animals are giraffes." However, Aristotle uses variables (e.g. "All A are B. Some B are C. Therefore, some A are C.
-This stuff all may seem obvious for us now in the modern-day, but it was a major breakthrough in the ancient world and forms the very basic foundation for logic as we understand it today.
-Allowed for Aristotle to state abstract arguments clearly as opposed to getting bogged down in confusing language.
-For example, he considers the problem: "All A is B." "No A is B." "Some A is B." "Some A is not B" (to make it easier for us, let's suppose that A=giraffes and B=animals).
-Aristotle analyzes these statements and their combinations to find that some of these combos will immediately produce a conclusion. If this is the case, these syllogisms are "complete". Others need some argument to produce a conclusion, while others are not productive at all.
-This is considered to be one of Aristotle's greatest achievements and sets the stage for 2000+ years of logic (it was only finally challenged in the 19th century by the German philosopher Gottlob Frege)!
-Aristotle knows that this is still a rather limited model, so he tries to demonstrate that all productive arguments can be reduced to these syllogisms (which was later refuted by the Stoics).
-Also spends a lot of time discussing the fact that the premises and conclusions of an argument can be either possible or necessary.
-For example, "Giraffes are necessarily mammals, and all mammals nurse their young." Does this mean that giraffes necessarily nurse their young? Does the necessity transfer from the premises to the conclusion?
-Aristotle believes that if a statement is necessarily true it must always be true. However, he also believed that if something was always true, then it was also necessarily true.
-But this doesn't make sense. For example, Peter Adamson doesn't have a sister and (unless he's mistaken and does SECRETLY have a sister) he will. However, is it necessarily true that he doesn't have a sister? That doesn't make sense.
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