Before the time of a famous Greek philosopher.
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The first known Western philosophers were the Presocratics, who lived in ancient Greece in the 6th and 5th centuries BC. Thales, Anaximander, and Heraclitus are some of the early philosophers who laid the foundations for Western philosophy.
Thales of Miletus is usually regarded as the first "philosopher". More particularly, he is the first of the Greek "Pre-socratic" philosophers (philosophers before Socrates). Thales and the other presocratics are sometimes called "sophists", and Socrates was a sort of anti-sophist who used a method of interrogation ("the elenchus") to reveal the ignorance and confusion behind the sophist's claims to knowledge. Against the sophists, who claimed to be wise, Socrates and his followers called themselves "philosophers", that is, "lovers of wisdom", to show that they were still trying to figure out the answers, and did not yet claim to have the final answers to everything.
The presocratics (or philosophers pre-Socrates) were primarily ontologists who rejected mythological explanations for reasoned discourse. Parmenides, for example, gave one of the first documented logical arguments: How could what is perish? How could it have come to be? For if it came into being, it is not; nor is it if ever it is going to be. Thus coming into being is extinguished, and destruction unknown. Heraclitus, in contrast to Parmenides' immutable one, asserted that the only thing that doesn't change and perish is change itself. As can be seen, then, the presocratics were concerned with what exists, where it comes from, what it comes from, how it exists and how the plurality of natural objects can be explained. Leucippus, against the monism of Parmenides, proposed an ontological pluralism with a cosmogony based on two main elements: the vacuum and atoms. These, by means of their inherent movement, are crossing the void and creating the real material bodies. Aristotle, Aristoteles in Latin and many other languages (but Aristote in French and Aristotele in Italian), (384 BC - 322 BC) has, along with Plato, the reputation of one of the most influential philosophers in history. Their works, although connected in many fundamental ways, differ considerably in both style and substance. Plato wrote several dozen philosophical dialogues-arguments in the form of conversations, usually with Socrates as a participant-and a few letters. Though the early dialogues deal mainly with methods of acquiring knowledge, and most of the last ones with justice and practical ethics, his most famous works expressed a synoptic view of ethics, metaphysics, reason, knowledge, and human life.
In general, it's meaning is simple and intuitive - the more similar a person is to oneself, the easier it is to get to know or understand that person. A second but related meaning of the phrase is knowing through analogy. This usage goes back at least to the Presocratics, especially Empedocles. Though it might seem to be used as a substitute for the phrase, "it takes one to know one", "like is known by like" is not normally used pejoratively like the former is. Another difference is that "it takes one to know one" does not seem to allow for degrees of likeness/knowledge. The concept of "like is known by like" was a major philosophical doctrine at least as early as the 5th century B.C.E. Pythagoras taught that the extent or depth of our knowledge of the divine depends on us being like the divine, or assimilating to the divine. The idea was that to the degree that we have knowledge of the divine, we must have changed our own character from human to divine. The doctrine of "like is known by like" was quite influential on later philosophical and religious schools of thought, especially Neoplatonism. One might also apply the phrase in ethics without referring to other minds (divine or otherwise), to mean "being good enables or helps one to know the good". The idea that virtue somehow illuminates moral truth suggests that more virtuous people have a greater ability to know moral truth.