Modal metaphysics

Dialetheism (; from Greek 'twice' and 'truth') is the view that there are statements that are both true and false. More precisely, it is the belief that there can be a true statement whose negation is also true. Such statements are called "true contradictions", dialetheia, or nondualisms.

the set of objects to which a term or concept applies

philosophical theory which holds that all possible worlds exist, and the actuality of our world is purely indexical

In analytic philosophy, actualism is the view that everything there is (i.e., everything that has being, in the broadest sense) is actual. Another phrasing of the thesis is that the domain of unrestricted quantification ranges over all and only actual existents.

Necessitarianism is a metaphysical principle that denies all mere possibility; there is exactly one way for the world to be.

concept in metaphysics