• Thales 624?-546? B.C., Greek philosopher who is traditionally considered the first Western philosopher and a founder of geometry and abstract astronomy.    He maintained that matter is composed of water.
• Heraclitus fl. 500 B.C., Greek philosopher who maintained that strife and change are natural conditions of the universe.    He believed that the universe was in a constant state of flux, or change.
• Parmenides born 515 B.C., Greek philosopher and a founder with Xenophanes of the Eleatic school holding the belief that immutable being is the only knowable reality and that change is the subject of mere opinion.    He claimed that the universe is unchanging.
• Democritus known as "the Laughing Philosopher," 460?-370? B.C., was a Greek philosopher who developed an atomist theory of the universe and espoused the doctrine that pleasure, along with self-control, is the goal of human life.    Atomism is the ancient theory of Democritus, Epicurus, and Lucretius, according to which simple, minute, indivisible, and indestructible particles are the basic components of the entire universe.
• Pythagoras a sixth century B.C., Greek philosopher and mathematician who founded in southern Italy a school that emphasized the study of musical harmony and geometry.    He proved the universal validity of the Pythagorean theorem and is considered the first true mathematician.    This school maintained that numbers were the true realities, and all other things in the universe were imitations of numbers.
• The Sophist were Greek philosophers of pre-Socratic times who inquired about and speculated on theology, metaphysics, mathematics, and the natural and biological sciences.    A professional philosopher and teacher, especially one belonging to a group of fifth-century B.C. Greek philosophers who specialized in dialectic, argumentation, and rhetoric and who were often known for their elaborate and specious arguments.
• Socrates 470?-399 B.C., Greek philosopher who initiated a question-and-answer method of teaching as a means of achieving self-knowledge.    His theories of virtue and justice have survived through the writings of Plato, his most important pupil. Socrates was tried for corrupting the minds of Athenian youth and subsequently put to death (399).    His famous maxim was "Know thyself." His chief task was to combat the Sophists.
• Plato 427?-347? B.C., Greek philosopher, and follower of Socrates, he founded the Academy (386), where he taught and wrote for much of the rest of his life.    Plato presented his ideas in the form of dramatic dialogues, as in the Republic.
• Aristotle 384-322 B.C., Greek philosopher, was a pupil of Plato, the tutor of Alexander the Great, and the author of works on logic, metaphysics, ethics, natural sciences, politics, and poetics, he profoundly influenced Western thought.    In his philosophical system theory follows empirical observation and logic, based on the syllogism, is the essential method of rational inquiry.    Syllogism is in Logic a form of deductive reasoning consisting of a major premise, a minor premise, and a conclusion; for example, All human beings are mortal, the major premise, I am a human being, the minor premise, therefore, I am mortal, the conclusion.    Reasoning from the general to the specific; deduction.    Aristotelian logic was Aristotle's deductive method of logic, especially the theory of the syllogism.    The formal logic based on Aristotle's and dealing with the relations between propositions in terms of their form instead of their content.    He did consider God as pure form, rather than as a personal Being who influences men's lives.

    After Aristotle, the Stoics and Epicureans concerned themselves with the rules of conduct.    The Romans followed in the Greek lines of thought.