Aristotle was a Greek philosopher and polymath who studied under Plato. He is considered one of the most important figures in Western philosophy. Aristotle emphasized syllogism and developed formal logic. He created the first formal system of reasoning. His major works include the Nicomachean Ethics, which discusses ethics as the science of good for human life. Aristotle concluded that critical thinking requires knowledge and the ability to assume things rightly. He is known for establishing the three principles of persuasion: logos, pathos, and ethos.