He is an expert in semiotics, and his theories are very profound.

He is an expert in ring theory and has written many papers in the field.

He is deepening his research on eschatology.

He was a fatalist, believing that all events are determined by fate.

He strongly advocated the hokushin theory.

He strongly advocated the theory of southward advancement.

We have developed a new methodology to solve this problem.

He believes in teleology, thinking that there is a meaning in every event.

Morphology is a part of linguistics that studies the structure of words.

Syntax is a branch of linguistics.