The Analogy of the Divided Line

What, then, becomes of those who attempt to gain knowledge by examining the natural world via sensory experience? According to Plato, they are doomed to ignorance or, at best, opinion. The only true knowledge involves grasping the forms themselves, and this can be done only by rational thought. Plato summarized this viewpoint with his famous analogy of the divided line.

Imagining is seen as the lowest form of under- standing because it is based on images—for exam- ple, a portrait of a person is once removed from the person. Reflections in the water are also images because they are a step removed from the objects reflected. We are slightly better off confronting the objects themselves rather than their images, but the best we can do even when confronting objects directly is to form beliefs or opinions about them. Beliefs, however, do not constitute knowledge. Still better is the contemplation of mathematical rela- tionships, but mathematical knowledge is still not the highest type because such knowledge is applied to the solution of practical (empirical) problems, and many of its relationships exist only by defini- tion. That is, mathematical relationships are assumed to be true, but these assumptions could conceiv- ably be false. To think about mathematics in the abstract, however, is better than dealing with images or empirical objects. The highest form of thinking be seen as anticipating many of the modern ideas of cognitive psychology with respect to matters such as concepts and conceptual categories. Plato’s answer was influenced by the Pythagorean notion of the immor- tality of the soul. According to the Pythagoreans, the highest form of thought was reason, which was a function of the immortal soul. Plato expanded this idea and said that before the soul was implanted in the body, it dwelled in pure and complete knowl- edge; that is, it dwelled in the realm of the forms. After the soul entered the body, sensory informa- tion began to contaminate this knowledge.