I. Aristotle’s life
• Born 384 B. C.
• Originally from Stagira in Macedonia
• Student of Plato
• Teacher of Alexander the Great
• Organized a school in Athens called the Lyceum which rivaled that of Plato
• When an anti-Macedonian movement swept Athens he left to avoid being executed (different from Socrates).
II. Plato and Aristotle
A. While Plato’s philosophy is idealistic, inspiring, otherworldly and perfectionist, Aristotle’s is realistic, scientific, this-worldly and pragmatic.
B. Styles are different largely in virtue of what has survived. Plato’s dialogues survived, Aristotle’s lecture notes survived.
C. Picture of the School of Athens: Plato points up (to the Forms), Aristotle point down (at the world of our experience).
Plato vs. Aristotle on knowledge
• For Plato the model for knowledge is mathematics. For Aristotle it’s biology. What’s the difference? Biology relies extensively on observation. E. Example: Plato’s social/political philosophy defines an ideal society. He doesn’t care if it’s attainable, and even tells you how it will fall apart if it is achieved. Aristotle’s looks at actual societies to see which ones work the best. He surveys 158 constitutions and decides which ones work the best in what circumstances.
III. All men by nature desire to know
• Theory of knowledge
• A. All human beings by nature desire to know.
• Do they? Or do we only desire that knowledge that will bring us pleasure?
• Presupposes that language and thought are congruent to the structure of reality. How could we understand nature if there is no affinity between nature and our minds?
Aristotle the Common sense philosopher
• For Plato there can be no science (rational discourse) of particular things. For Aristotle there can be, in fact knowledge begins with the study of particular things. So the marker in my hand is not an object of knowledge, only belief. Aristotle found this preposterous.
IV. There are real physical objects, by golly
• Aristotle maintains that it is a mistake to study an abstract quality in isolation form concrete exemplifications. Thus Aristotle presumes that we can know particular things. In fact, while this seems like a pretty common-sense idea, philosophers from the Eleatics (those who denied motion) to the atomists (it’s all really atoms, not particular things) to the Sophists (there’s no knowledge) to Plato (all we can really know are forms), denied this common-sense notion.
V. The presuppositions of knowledge
• Aristotle presupposes that language and thought are congruent to the structure of reality. How could we understand nature if there is no affinity between nature and our minds? Otherwise, we coudn't negotiate traffic on 59th Avenue during rush hour.
VI. Aristotle’s ten categories
• 1. What is it?
2. How large is it?
3. What is it like?
4. How is it related?
5. Where is it?
6. When does it exist?
7. What position is it in?
8. What condition is it in?
9. What is it doing?
10. How is it acted upon?
Would Plato ask these questions, and expect an answer?
VII. Aristotle discovers logic
• Logic is the science of arguments. Aristotle discovered that you could distinguish the form of an argument from the content of the argument. Aristotle put statements into categories and show how you can determine, based on the structure of an argument, whether or not the argument is valid.
VIII. The concept of validity
• 1. An argument is valid, just in case, on the assumption that the premises are true, the conclusion must be true. If an argument is valid, the internal logic of the argument is solid. The argument can only be challenged externally, but attacking the truth of the premises. Aristotle’s key discovery is that arguments can be analyzed from the point of view of their logical form, as well as from the point of view of the truth of the premises.
IX. An example of a valid argument
• 1. All dogs are mammals.
• 2. No mammals are birds.
• 3. Therefore no dogs are birds.
• No matter how you change the premises of this argument you cannot get an argument that has true premises and a false conclusion.
X. Validity is a matter of logical form (repeat this ten times).
• Validity is a matter of logical form. A valid argument can be given in favor of a false conclusion, or even in favor of a stupid conclusion. (Also repeat this ten times).
XI. This argument, for example, is valid
• 1. The moon is made of green cheese.
• 2. If the moon is made of green cheese, then the moon is made of red cheese.
• 3. Therefore the moon is made of red cheese.
• The conclusion is false, but so are the premises. If you were to retain the logical structure but change the terms of the argument, you could never get true premises and a false conclusion.
XII. Invalid arguments
Other argument forms do not reliably get true conclusions if the premises are true. There are invalid arguments.
An argument can have true premises and true conclusions and still be a bad argument because the logical structure is faulty
Ex. All beagles are dogs.
All hounds are dogs.
Therefore all beagles are hounds.
Although this argument has true premises and a true conclusion, it is nevertheless an invalid (and therefore bad) argument, because by the same logic the same argument could just as easily support the conclusion “All beagles are hounds” a clear falsehood.
XIII. Sound Arguments
• A sound argument is a valid argument with true premises.
• If the premises are true and the argument is valid, and the conclusion is guaranteed to be true.
XIV. Inductive Arguments
• Some arguments don’t have to be valid to be good.
• 1) In the past, the sun has always risen in the morning.
• 2) Therefore, the sun will rise tomorrow.
XV. First Principles
• Aristotle maintained that there were certain fundamental principles in every discipline. Although some people would like to think they can, or should, prove everything they believe, Aristotle realized that you can demand proof for the premises every time proof is offered, and impose an infinite regress. Some things are so basic as not to require proof.
XVI. The Law of Non-Contradiction
• An example would be the law of noncontradiction in logic, the claim that a statement and its contradictory cannot both be true. The trouble here is that any argument for the law of noncontradiction is going to assume the law of noncontradiction, and thereby be open to charge of being a circular argument. However, if someone doesn’t believe in the law of noncon, Aristotle will ask “Are you really saying that?” If the person says they are making a statement, then Aristotle will say that the person has implicitly accepted the law of non-contradiction. If the person says “No, I’m not really saying that,” then Aristotle says “Well, if you aren’t really saying anything, then I really have nothing to respond to,” and treat the person as a cabbage.