In informal logic
Informal logic, intuitively, refers to the principles of logic and logical thought outside of a formal setting. However, perhaps because of the informal in the title, the precise definition of informal logic is matters of some dispute. Ralph H. Johnson and J...
, a reason
consists of either a single premise
Premise can refer to:* Premise, a claim that is a reason for, or an objection against, some other claim as part of an argument...
A co-premise is a premise in reasoning and informal logic which is not the main supporting reason for a contention or a lemma, but is logically necessary to ensure the validity of an argument...
s in support of an argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...
. In formal symbolic logic
In philosophy, Logic is the formal systematic study of the principles of valid inference and correct reasoning. Logic is used in most intellectual activities, but is studied primarily in the disciplines of philosophy, mathematics, semantics, and computer science...
, only single premises occur. In informal reasoning, two types of reasons exist. An evidential reason
is a foundation upon which to believe that
a claim is true. An explanatory reason
attempts to convince you how
something is or could be true, but does not directly convince you that it is
In contrast to reason
Reason is a term that refers to the capacity human beings have to make sense of things, to establish and verify facts, and to change or justify practices, institutions, and beliefs. It is closely associated with such characteristically human activities as philosophy, science, language, ...
as an abstract noun, a reason
is a consideration which explains or justifies. Philosophers often distinguish explanatory
reasons from normative
are considerations which serve to explain why things have happened—they are reasons why
events occur, or why states of affairs are the way they are. In other words, "reason" can also be a synonym for "cause". For example, a reason why a car starts is that its ignition is turned. In the context of explaining the actions of beings who act for reasons (i.e., rational agents), these are called motivating reasons
—e.g., the reason why Bill went to college was to learn; i.e., that he would learn was his motivating reason. At least where a rational agent is acting rationally, her motivating reasons are those considerations which she believes count in favor of her so acting.
, on the other hand, are often said to be "considerations which count in favor" of some state of affairs (this is, at any rate, a common view, notably held by T.M. Scanlon and Derek Parfit
Derek Parfit is a British philosopher who specializes in problems of personal identity, rationality and ethics, and the relations between them. His 1984 book Reasons and Persons has been very influential...
). Some philosophers (one being John Broome
John Broome is a British philosopher and economist. He is currently the White's Professor of Moral Philosophy at the University of Oxford and a Fellow of Corpus Christi College, Oxford....
) view these as the same as "explanations of ought facts". Just as explanatory reasons explain why some descriptive fact obtains (or came to obtain), normative reasons on this view explain why some normative facts obtain, i.e., they explain why some state of affairs ought to come to obtain (e.g., why someone should act or why some event ought to take place).
A common philosopher's distinction concerning normative reasons is between epistemic reasons
and practical reasons
. Epistemic reasons (also called theoretical
reasons) are considerations which count in favor of believing some proposition to be true. Practical reasons are considerations which count in favor of some action or the having of some attitude (or at least, count in favor of wanting or trying to bring those actions or attitudes about).