ARISTOTLE ON LOGIC
- Logic as a "tool:" the
ORGANON
- Demonstration:
- explanation takes the form of argument
- arguments & argument forms
- towards the concept of "validity"
- demonstrations as valid arguments from sound premises
- The six books of the
ORGANON:
- The Categories:
- classifying words by the kinds of things they refer to
- substance ("a human being," "a horse")
- quantity ("two cubic meters," "100 kilometers")
- quality ("red," "taught," "bold," "dry")
- relation ("triple," "one-third")
- place ("on the acropolis," "in the Pireaus")
- position ("is lying down," "is standing upright")
- having ("is clothed," "is armed")
- acting ("burns," "cuts")
- being acted upon ("is burned," "is cut")
- logical properties of words in each category (substance, for example, has not opposite; most qualities admit of variation in degree, etc.)
- the chief meanings of certain crucial terms, like "opposite," "prior," and "motion"
- On Interpretation
Aristotle's account of simple sentences (what later come to be called "propositions." Deals with quantifiers ("all," "some," "none") and their logical relations.
- Prior Analytics
Aristotle's anaylsis of the simplest form of argument: the three-term Syllogism. The standard example in philosophy has always been:
- All men are mortal. [Premise1 in the form:
All B's are C's.]
- Socrates is a man. [Premise 2 in the form:
(All) A is B.]
- Therefore, Socrates is mortal. [Conclusion in the form:
All A's are C's.]
This example is somewhat misleading, despite the fact that it is the standard one, since it treats a proper name ("Socrates") as a term (or class name.) One of the fundamental departures of modern (19th & 20th Century C.E.) symbolic logic is that it treats sentences about individuals differently from the way it treats sentences about classes. But with this first figure form of the syllogism Aristotle arrives at a clear and explicit distinction between truth and validity, where the latter is a property of argument forms. (If the premises of a valid argument are true, the conclusion must be true.)
- Posterior Analytics
Here Aristotle identifies the valid forms of the syllogism. He identifies the formal key to valid syllogistic forms in the middle term (identified in the form above by "B.") The middle term must be "distributed" (quantified) if an argument form is to be valid. (Of course this is a necessary but not sufficient condition. Not every argument form with a distributed middle term is valid.)
For a syllogism to achieve the status of a demonstration the argument form must be valid and the premises must be true, and must be known to be true unconditionally. The premises must, therefore, either be themselves derivable as conclusions of other demonstrations following necssarily from necessarily true premises or they must be known by "intuition" (NOUS.)
- Topics
The "Topics" identify strategies and techniques Aristotle indentified for constructing valid arguments. The general name for this kind of reasoning is dialectic. Dialectic begins with a opinion or belief, examines, criticizes, and revises that opinion/belief in the light of reason and other things known or believed to be true, in order to establish scientifically known premises which can then be used in demonstrations to generate syllogistically the truth of consulsions dervived. Aristotle's account of dialectic owes much to the "method of hypotheses" in Plato's Phaedo.
- On Sophistical Refutations
Deals with a variety of bad or invalid argument forms: "fallacies"
Revised November 10, 1996
Index to Study Guides to Aristotle
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