Although Plato is considered by most to be the father of philosophy, he did not create the field out of nothing. There already existed several currents of thought, which were prominent at the time in which Plato was writing and which were influential to his thought. Plato’s travels in southern Italy and Sicily as a young man brought him into close contact with many followers of the philosopher Pythagoras, whose mathematical research played an important role in Plato’s early intellectual development. Plato was also familiar with and influenced by the philosophy of Heraclitus, who claimed that the world was in constant flux. Plato was also influenced to write against the relativist ideas advocated at the time by Protagoras and the materialist mode of explanation assumed by Democritus.

However, the most important influence on Plato is obviously that of his mentor, Socrates. Aside from other strains of philosophy popular at the time, there were also several periods and methods present within the entire philosophy of Plato. Generally, Plato's dialogues are classed into categories of early, middle, and late periods. The early dialogues were written soon after Socrates’s death, and in them we get the clearest picture of Socrates and Socratic philosophy. As Plato matured, however, he developed an increasingly distinct voice and philosophical outlook.

The figure of Socrates in the middle dialogues (including The Republic) and later dialogues is more of a mouthpiece for Plato’s own views. In particular, the theory of Forms, we know from Aristotle, was not a belief held by the actual Socrates, despite the fact that his character preaches it consistently in many of the middle and later dialogues. The Laches is considered to be one of Plato's early dialogues. Other early dialogues include The Apology, Crito, Phaedo, and Euthyphro—together comprise the quartet of Plato’s works that are sometimes collectively called The Trial and Death of Socrates.