Philosophy is a Tier Three technology that unlocks the Mind Bender, a unit that can heal friendly units and convert enemy units; the Genius Task, which grants the Tower of Wisdom once all of the technologies are researched; and the literacy bonus, which reduces the cost of all technologies by 20% (final costs rounded up).
Philosophy can only be researched after Meditation has been researched.
Philosophy was introduced in the "Power" update. In beta, Philosophy unlocked the Library, a building that decreased the costs of technologies. The Library was scrapped and replaced by the Literacy Bonus.