Philosophy of logic

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 the philosophy of logic and philosophical logic is of recent coinage and not always entirely clear. Characterisations include:
This article outlines issues in philosophy of logic or provides links to relevant articles or both.
Introduction.
This article makes use of the following terms and concepts:
Truth.
Aristotle 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.
Truthbearers.
Logic uses such terms as true, false, inconsistent, valid, and self-contradictory. Questions arise as Strawson (1952) writes
Tarski's definition of truth.
See:
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:
The concept of logical truth is intimately linked with those of validity, logical consequence and entailment (as well as self-contradiction, necessarily false etc.).
Issues that arise include:
See also 
Meaning and reference.
See
See also.
Important figures.
Figures in the philosophy of logic include (but are not limited to):