Philosophy is the study of fundamental problems concerning existence, knowledge, values, reason, and language. Pre-Socratic philosophers were primarily concerned with cosmology and rejected mythological explanations in favor of reasoned discourse. In the 5th century BCE, Greek philosophy began to direct its thinking towards human life due to lack of proof for cosmological assertions. This led to the emergence of the Sophists who argued that truth and morality were relative. Socrates pursued rational thought to discover philosophical absolutes, in disagreement with the Sophists' view of relative truth.