  This approach centers on the truthmaker or truthmaking principle: Every truth has a truthmaker; or alternatively: For every truth there is something that makes it true. The principle is usually understood as an expression of a realist attitude, emphasizing the crucial contribution the world makes to the truth of a proposition. Advocates tend to treat truthmaker theory primarily as a guide to ontology, asking: To entities of what ontological categories are we committed as truthmakers of the propositions we accept as true? Most advocates maintain that propositions of different logical types can be made true by items from different ontological categories: e.g., propositions of some types are made true by facts, others just by individual things, others by events, others by tropes (cf., e.g. Armstrong 1997). This is claimed as a significant improvement over traditional correspondence theories which are understood—correctly in most but by no means all cases—to be committed to all truthmakers belonging to a single ontological category (albeit disagreeing about which category that is). All advocates of truthmaker theory maintain that the truthmaking relation is not one-one but many-many: some truths are made true by more than one truthmaker; some truthmakers make true more than one truth. This is also claimed as a significant improvement over traditional correspondence theories which are often portrayed as committed to correspondence being a one-one relation. This portrayal is only partly justified. While it is fairly easy to find real-life correspondence theorists committing themselves to the view that each truth corresponds to exactly one fact (at least by implication, talking about the corresponding fact), it is difficult to find real-life correspondence theorists committing themselves to the view that only one truth can correspond to a given fact (but see Moore 1910-11, p. 256).