A Logic Tool of Learning

The purpose of classical education is to provide students with tools of learning. One of the most useful tools is the genus and species chart. I have used this tool in every course I have taught: Logic, Rhetoric, Calculus, Physics, and Doctrine.

For example, in my rhetoric course, my students and I construct the genus and species chart shown below, to organize the seven causes of actions presented by Aristotle in his Rhetoric I.10:

Causes of actions chart

This clearly shows that every action is the result of one or more of these seven causes: habit, rational craving, anger, appetite (voluntary actions – used for prosecution); chance, compulsion, nature (involuntary actions – used for defense). This visual aid is much clearer than the wordy paragraph given in the text. I use a similar chart in Calculus to present the types of functions, in Physics for the branches of physics, and in Doctrine for the “Liar, Lunatic, Lord” argument for the deity of Jesus.

When teaching this tool in Logic one should insist on a clear dividing principle between species, to avoid species overlapping or being placed at the wrong level. In the above chart, the top dividing principle is “whether or not the action is due to oneself.” Under involuntary actions, the dividing principle between chance and necessity is “whether or not the cause is fixed and determined”; under necessity, the dividing principle between compulsion and nature is “whether it is external or internal.” The dividing principles between habit and craving or between anger and appetite are less clear, though the dividing principle under craving is obvious.

I used this tool in my Logic class today as I taught the difference between supported  and self-supporting statements. The dividing principle is “how the truth value is determined.” I would encourage logic teachers to use this tool often, both to present the lesson clearly and to train the students in the use of the tool.


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