Logic
Logic, or the study of the principles of proper resoning, was pioneered by Aristotle. Although it is possible that Aristotle himself had been tought by someone else, the earliest records we have of the codification of studying reasoning can be attributed to Aristotle.
Logic as a science defines the structure of statement and argument, and defines formulae by which these are codified. Implicit in a study of logic is the understanding of what makes a good argument, and what arguments are fallacious. Students of classical logic were often made to memorize certain argument forms so that they could more easily create better arguments and disprove weaker ones thrown against them. The Jesuits emphasized this so highly, that their students were required to take part in a structured argument session with their peers.
The ultimate goal of Logic is clarity. By making correct reasoning into a science, Logic seeks to put an end to the indecisiveness of argument and statement.