Human behavior flows from three main sources: desire, emotion, and knowledge. ~ Plato
Plato (427–347 bce) was Socrates’ student and successor. He surpassed his teacher by laying the foundations of Western philosophy and science. After Socrates death and an extended spell in Italy, where he came under the influence of the Pythagoreans, Plato founded his academy in Athens.
Plato explained sensation and perception as the transformation of actuality into what he called forms. According to Plato’s theory of forms, everything in the empirical world is an inferior, passing manifestation of pure forms, which themselves have an independent, intemporal existence.
To Plato perceptions are flickering shadows of which surety is impossible. Although lacking incarnation, forms are the real thing.
Though the soul is implanted in a body, it still dwells with forms: pure and complete knowledge. The only way to arrive at true knowledge is to ignore perceptions and concentrate on insights accessible only through intuition.
Plato proposed the soul as a tripartite construction: the rational as the immortal seat of reason, the emotional (spirited), and the appetitive as the source of desire. There is a built-in conflict between the 3 in how to spend time and expend energy.
For Plato, the supreme aspiration in life is freeing the soul as much as possible from the adulterations of the flesh. This lofty aim followed the Pythagorean tradition.
Plato’s reminiscence theory of knowledge posited that all knowledge was innate and can only be tapped through introspection. As all information is carried within the soul, knowledge is attained via reminiscence: remembering the past experiences of the soul. Sensory experience can only remind one of what is already known.
The soul, since it is immortal and has been born many times, and has seen all things both here and in the other world, has learned everything that is. So, we need not be surprised if it can recall the knowledge or virtue of anything else which, as we see, it once possessed. All Nature is akin, and the soul has learned everything, so that when a man has recalled a single piece of knowledge there is no reason why he should not find out all the rest, if he keeps a stout heart and does not grow weary of the search, for seeking and learning are in fact nothing but recollection. ~ Plato in Meno
A few labels may be laid upon Plato’s epistemology: idealism, rationalism, and nativism. Idealism asserts that reality – as far it can be understood – is fundamentally a mental construction. Rationalism regards reason as the source of knowledge, obtained via deduction. Nativism nestles knowledge as innate.
Plato recognized individual differences in talents, skills, and aptitudes. In the Republic (~380 bce) Plato sketched a utopian society with an oligarchical government comprising those of superior reasoning, ruled by a philosopher-king.
Properly populating the ideal society necessitates assessment of those to serve various roles. To Plato, the traits suited for different occupations could be measured. Plato believed such qualities were localized in different body parts: reason in the head, courage in the chest, appetite in the abdomen. This phrenology anticipated psychometrics: the study of measuring psychological qualities.