Only propositions were considered "truth-bearers" or "truth-vehicles" (i.e., they could be called true or false) while sentences were simply their vehicles of expression.
Different lektá could also express things besides propositions, such as commands, questions and exclamations.
He criticized conventionalism because it led to the bizarre consequence that anything can be conventionally denominated by any name.
Hence, it cannot account for the correct or incorrect application of a name.
It overlaps to some extent with the study of Epistemology, Logic, Philosophy of Mind and other fields (including linguistics and psychology).
In a broader sense it may be said that the philosophy of language explores the relationship between language and reality.
He separated all things into categories of species and genus.
He thought that the meaning of a predicate was established through an abstraction of the similarities between various individual things. However, since Aristotle took these similarities to be constituted by a real commonality of form, he is more often considered a proponent of "moderate realism".
There is a tradition called speculative grammar which existed from the 11th to the 13th century.
Leading scholars included, among others, Martin of Dace and Thomas of Erfurth.