Plato (428/427–348/347 B.C.)
“The only real ill-doing is the deprivation of knowledge.”

Best-known work: The Republic.

Big ideas: Theory of Forms; platonic relationship.

• Everything on earth, whether an object (such as a car) or an idea (such as justice), is actually an imperfect copy of an ideal and permanent “form” that exists somewhere, beyond our universe. This is known as the Theory of Forms. The place where all these ideal forms exist is guided by a heavenly force that Plato believed should influence our behavior. (This notion shaped Christianity.) The ideal that was the most important to Plato was moral goodness, which he called “the good.” He believed that we should spend our lives trying to attain absolute goodness, even if we always fall short, because it is the path to happiness.
• Plato believed that the ideal version of love is a meeting of the minds and doesn’t entail a physical aspect―hence the term “platonic relationship.”

Plato today: Plato was the original perfectionist, but he also understood that utter perfection is an unattainable goal. So when you’re cleaning the kitchen, you may strive to reach an operating-room level of cleanliness, but even Plato would have been able to live with a few stray crumbs.

Aristotle (384–322 B.C.)
“Anything that we have to learn to do, we learn by the actual doing of it.”

Best-known work: Nicomachean Ethics (supposedly named after Aristotle’s son, Nicomachus).

Big ideas: Deductive reasoning; golden mean; catharsis.

• When a person truly understands a topic, she can create a deductive argument―one that starts with a general concept and works toward a more specific one. Aristotle favored a type of deductive reasoning called syllogism (also a favorite of Sherlock Holmes), in which two premises are combined to reach a conclusion: All men are mortal. George Clooney is a man. Therefore George Clooney is mortal. (Although that might be hard to believe.)
• Life should be lived according to the “golden mean”―what Aristotle called the virtuous halfway point between two vices. For example, courage is the mean between cowardice and rashness.
• The emotional cleansing one experiences while watching a dramatic performance is what Aristotle termed “catharsis.” For example, you might have had a cathartic moment, with mixed feelings of hope and despair, when Kate Winslet delivered the line “I’ll never let you go, I promise” to a dying Leonardo DiCaprio in Titanic (if you weren’t busy looking at your watch).

Aristotle today: When trying to balance demands of work and home, consider Aristotle’s golden mean: If you’re a slave to a PDA and a cell phone, your family life will suffer. But ignore the devices and you may be out of a job. Switching them off for a few well-chosen hours daily might keep everyone happy.