1. in logic, a proposition to be subjected to logical analysis in the interest of proof or disproof.

2. more generally, any idea or proposition put forward in argumentation.

3. in philosophy, the first stage of a dialectical process: a proposition that is opposed by an antithesis, thereby generating a new proposition referred to as a synthesis. The synthesis serves as thesis for the next phase of the ongoing process. This use of the term is associated particularly with the work of German philosopher Georg Wilhelm Friedrich Hegel (1770–1831). See also dialectical materialism.

4. a dissertation based on original research, especially one required for an advanced academic degree.