Following the developments in formal logic with symbolic logic in the late nineteenth century and mathematical logic in the twentieth, topics traditionally treated by logic not being part of formal logic have tended to be termed either philosophy of logic or philosophical logic if no longer simply logic.
Compared to the history of logic the demarcation between philosophy of logic and philosophical logic is of recent coinage and not always entirely clear. Characterisations include
Philosophy of logic is the area of philosophy devoted to examining the scope and nature of logic.
Philosophy of logic is the investigation, critical analysis and intellectual reflection on issues arising in logic. The field is considered to be distinct from philosophical logic.
Philosophical logic is the branch of study that concerns questions about reference, predication, identity, truth, quantification, existence, entailment, modality, and necessity.
Philosophical logic is the application of formal logical techniques to philosophical problems.
This article outlines issues in philosophy of logic or provides links to relevant articles or both.
(a) when we use these words of logical appraisal, what is it exactly that we are appraising? and (b) how does logical appraisal become possible?
This article makes use of the following terms and concepts:
Type–token distinction
Use–mention distinction
Parmenides said To say that that which is, is not or that which is not is, is a falsehood; and to say that which is, is and that which is not is not, is true
This apparent truism has not proved unproblematic.
Logic uses such terms as true, false, inconsistent, valid, and self-contradictory. Questions arise as Strawson (1952) writes
(a) when we use these words of logical appraisal, what is it exactly that we are appraising? and (b) how does logical appraisal become possible?
See also: Sentence, Statement, Proposition.
See:
Semantic theory of truth § Tarski's Theory
T-schema
Stanford Encyclopedia of Philosophy entry on Tarski's Truth Definitions
Self-reference:2.1 Consequences of the Semantic Paradoxes in Stanford Encyclopedia of Philosophy
Analytic truths, logical truth, validity, logical consequence and entailment
Since the use, meaning, if not the meaningfulness, of the terms is part of the debate, it is possible only to give the following working definitions for the purposes of the discussion:
A necessary truth is one that is true no matter what the state of the world or, as it is sometimes put, in all possible worlds.
Logical truths are those necessary truths that are necessarily true owing to the meaning of their logical constants only.
In formal logic a logical truth is just a "statement" (string of symbols in which no variable occurs free) which is true under all possible interpretations.
An analytic truth is one whose predicate concept is contained in its subject concept.
The concept of logical truth is intimately linked with those of validity, logical consequence and entailment (as well as self-contradiction, necessarily false etc.).
If q is a logical truth, then p therefore q will be a valid argument.
If p1, p2, p3 ... pn therefore q is a valid argument then its corresponding conditional will be a logical truth.
If p1 & p2 & p3 ... pn entails q then If (p1 & p2 & p3 ... pn) then q is a logical truth.
If q is a logical consequence of p1 & p2 & p3 ... pn if and only if p1 & p2 & p3 ... pn entails q and if and only if If (p1 & p2 & p3..pn) then q is a logical truth
Issues that arise include:
If there are truths that must be true, what makes them so?
Are there analytic truths that are not logical truths?
Are there necessary truths that are not analytic truths?
Are there necessary truths that are not logical truths?
Is the distinction between analytic truth and synthetic truth spurious?
See also [1]
Names and descriptions
Failure to refer
Proper name (philosophy)
Definite description
Descriptivist theory of names
Theory of descriptions
Singular term
Term logic § Singular terms
Empty name
Bas van Fraassen § Singular Terms, Truth-value Gaps, and Free Logic
The Foundations of Arithmetic § Development of Frege's own view of a number
Philosophy of language § references
Direct reference
Mediated reference theory
The problem of the material conditional: see Material conditional
Conceptualism
Constructivism
Dialetheism
Fictionalism
Finitism
Formalism
Intuitionism
Logical atomism
Logicism
Nominalism
Realism
Platonic realism
Structuralism
Leibniz's Law: see Identity of indiscernibles
Vacuous names
Do predicates have properties?: See Second-order logic
Sense, Reference, Connotation, Denotation, Extension, Intension
The status of the Laws of Logic
Classical Logic
Intuitionism
Realism: see Platonic realism, Philosophical realism
The Law of Excluded Middle: see Law of excluded middle
Modality, Intensionality and Propositional Attitude
Counter-factuals
Psychologism
