While Socrates may or may not have, as Plato contended, defined man as a "featherless biped," Socrates definitely defined man as the species that creates ideas. Men thrive on ideas and live by their wits, not their brute strength. The great question for Socrates then became: what kind of ideas will men come up with? Will they be sensible ideas, based on reason, or will they be silly? Since man is primarily a creature of deliberative thought, it followed that focusing on developing the best ideas—on the processes of thought, cognition and self awareness—would create the greatest wisdom and hence better men. Socrates put an emphasis not on technological innovation or sensory perception but developing cognitive ideas that bring us closer to justice, freedom, beauty, and truth.
In the Phaedo Socrates argued that the external senses do not bring us closer to truth. Instead we should be concerned not with the body but with the soul. In fact the human body (our status as "featherless bipeds") does not define us as men (sadly, Socrates is thinking in a gendered way) but, in fact, human appetites and desires for food, comfort, wealth, and physical things interfere with developing man's fullest humanity.
While Socrates defined men as limited and therefore not capable of reaching absolute truth, he also believed they had immense capability for attaining an ever more refined idea of the just and the good. This awareness and definition of man as primarily a thinking being is the basis of Western philosophy.
Socrates’ teachings indicate that man is uniquely defined through his ability to think and question his own existence. Socratic philosophy centers around the claim that man has the ability to examine himself through dialogue with others and that "the unexamined life is not worth living."
This definition aligns with Socrates’ insight that man thrives when he feeds his inner soul with knowledge as opposed to the temporary indulgence of shallow, physical pursuits. This philosophic argument maintains that questioning belief systems will ultimately result in deeper self-knowledge. In turn, Socrates argues, wisdom gained from deconstructing one another's belief systems will ultimately lead to a cleansing of the soul, wherein the virtues of truth can be extracted with ever increasing clarity and complexity.
To Socrates, the pursuit of excellence in thoughtful contemplation defines the quality of life a man can lead.