Reason ~ involves the ability to think, understand and draw conclusions in an abstract way. It is often felt to be objective or neutral concerning the understanding of reality it can be used to develop, and is thus contrasted with emotionalism, which is thinking driven by desire, passion, or prejudice. Reason is a conscious attempt to discover what is true and what is best. Reason often follows a chain of cause and effect, and the word "reason" can be a synonym for "cause".

Reason and logic can be thought of as distinct, although logic is one important aspect of reason. Author Douglas Hofstadter, in Gödel, Escher, Bach, characterizes the distinction in this way. Logic is what is done "inside the system" by formal steps such as deduction. Reason is what is done "outside the system" by such informal methods as skipping steps, working backward, drawing diagrams, looking at examples, or seeing what happens if you change the rules of the system. In the present day there is an increasing tendency to use the terms interchangeably, or to see logic as the most pure or the defining form of reason.

Neurologist Terrence Deacon, following the tradition of Charles Peirce, has recently given a useful new description of what makes reason distinctive compared to logic, as well as the information processing of computers and at least most animals, in modern terms. Like many philosophers in the English tradition, such as Hobbes, Locke, and Hume, Peirce starts by distinguishing the type of thinking which is most essential to human reason as a type of associative thinking. Reason, by his account, requires associating perceptions with icons. For example, the mind may associate the image (or icon) of smoke with not only the image of fire, but may also associate the word "smoke", or indeed any made-up symbol, with the image of fire.

Logic ~ is the study of the principles of valid demonstration and inference. The word derives from Greek "logike" "possessed of reason, intellectual, dialectical, argumentative", from logos, "word, thought, idea, argument, account, reason, or principle".

As a formal science, logic investigates and classifies the structure of statements and arguments, both through the study of formal systems of inference and through the study of arguments in natural language. The field of logic ranges from core topics such as the study of validity, fallacies and paradoxes, to specialized analysis of reasoning using probability and to arguments involving causality. Logic is also commonly used today in argumentation theory.

Traditionally, logic is considered a branch of philosophy, a part of the classical trivium of grammar, logic, and rhetoric. Since the mid-nineteenth century formal logic has been studied in the context of foundations of mathematics,
where it was often called symbolic logic. In 1879 Frege published Begriffsschrift : A formula language or pure thought modelled on that of arithemetic which inaugurated modern logic with the invention of quantifier notation. In 1903 Alfred North Whitehead and Bertrand Russell attempted to establish logic formally as the cornerstone of mathematics with the publication of Principia Mathematica.[4] However, except for the elementary part, the system of Principia is no longer much used, having been largely superseded by set theory. At the same time the developments in the field of Logic since Frege, Russell and Wittgenstein had a profound influence on both the practice of philosophy and the ideas concerning the nature of philosophical problems especially in the English speaking world (see Analytic philosophy). As
the study of formal logic expanded, research no longer focused solely on foundational issues, and the study of several resulting areas of mathematics came to be called mathematical logic. The development of formal logic and its
implementation in computing machinery is fundamental to computer science. Logic is now widely taught by university philosophy departments, more often than not as a compulsory discipline for their students, especially in English speaking world.