Concept
Logical truth
Overview
Logical truth is one of the most fundamental concepts in logic. Broadly speaking, a logical truth is a statement which is true regardless of the truth or falsity of its constituent propositions. In other words, a logical truth is a statement which is not only true, but one which is true under all interpretations of its logical components (other than its logical constants). Thus, logical truths such as "if p, then p" can be considered tautologies. Logical truths are thought to be the simplest case of statements which are analytically true (or in other words, true by definition). All of philosophical logic can be thought of as providing accounts of the nature of logical truth, as well as logical consequence.
Logical truths are generally considered to be necessarily true. This is to say that they are such that no situation could arise in which they could fail to be true. The view that logical statements are necessarily true is sometimes treated as equivalent to saying that logical truths are true in all possible worlds. However, the question of which statements are necessarily true remains the subject of continued debate.
Treating logical truths, analytic truths, and necessary truths as equivalent, logical truths can be contrasted with facts (which can also be called contingent claims or synthetic claims). Contingent truths are true in this world, but could have turned out otherwise (in other words, they are false in at least one possible world). Logically true propositions such as "If p and q, then p" and "All married people are married" are logical truths because they are true due to their internal structure and not because of any facts of the world (whereas "All married people are happy", even if it were true, could not be true solely in virtue of its logical structure).
Rationalist philosophers have suggested that the existence of logical truths cannot be explained by empiricism, because they hold that it is impossible to account for our knowledge of logical truths on empiricist grounds. Empiricists commonly respond to this objection by arguing that logical truths (which they usually deem to be mere tautologies), are analytic and thus do not purport to describe the world. The latter view was notably defended by the logical positivists in the early 20th century.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
Possible passages
Found by search and not yet checked by a person; they may only mention the idea in passing.
_On the contrary,_ It is written (Ps. 11:2), "Truths are decayed from among the children of men." _I answer that,_ Truth, properly speaking, resides only in the intellect, as said before (A. 1); but things are called true in virtue of the truth residing in an intellect. Hence the mutability of truth must be regarded from the point of view of the intellect, the truth of which consists in its conformity to the thing…
Aquinas Thomas, Summa Theologica, Part I
States what Logical truth is; the author is tied to Logical truth in the knowledge graph.
That ‘to be true’ _means_ to be thought in a certain way is, therefore, certainly false. Yet this assertion plays the most essential part in Kant’s ‘Copernican revolution’ of philosophy, and renders worthless the whole mass of modern literature, to which that revolution has given rise, and which is called Epistemology. Kant held that what was unified in a certain manner by the synthetic activity of thought was _ipso…
G. E. Moore, Principia Ethica
States what Logical truth is.
of speech, only to PROPOSITIONS: yet IDEAS are oftentimes termed true or false (as what words are there that are not used with great latitude, and with some deviation from their strict and proper significations?) Though I think that when ideas themselves are termed true or false, there is still some secret or tacit proposition, which is the foundation of that denomination: as we shall see, if we examine the…
John Locke, An Essay Concerning Humane Understanding, Volume 1
States what Logical truth is.
Philosophers who discussed Logical truth
- G. E. Moore
- David Kaplan (philosopher)
- Karl Popper
- Francis Hutcheson (philosopher)
- William Whewell
- Thomas Aquinas
- Chrysippus
- Imre Lakatos
- David Lewis (philosopher)
- Saul Kripke
- Robert Audi
- Rudolf Carnap
- Charles Hartshorne
- Edmund Husserl
- Ernst Mally
- Nathan Salmón
- Michael Foster (philosopher)
- Jerome Inglott
Related ideas
- Empiricism
- First-order logic
- If and only if
- Negation
- Truth value
- Logical conjunction
- Logical connective
- Propositional logic
- Logical positivism
- A. J. Ayer
- False (logic)
- Knowledge
- Rule of inference
- Sheffer stroke
- Truth
- Philosophical logic
- Language, Truth, and Logic
- Willard Van Orman Quine
- Logical consequence
- Nonsense
- Formal system
- Well-formed formula
- Logical constant
- Quantifier (logic)
Opposing perspectives
Place in the tradition
Part of Analytic philosophy.