θέσις

Thésis comes from the Greek verb tithénai (to place, to put, to set down). A thesis was something placed — a proposition set before an audience for debate. In Aristotle's usage, a thesis was a statement that contradicted popular opinion and therefore required defense. The word carried risk: to place a thesis was to place yourself in opposition. It was not a summary of existing knowledge. It was a challenge.

Medieval universities adopted the thesis as a formal examination format. A student who wished to earn a degree had to defend a thesis — literally stand in a hall and argue for a proposition against the attacks of examining masters. The thesis defense (disputatio) was a public event. The community watched. The student either won or did not. Martin Luther's 95 Theses, posted (or mailed) in 1517, used the academic format for religious revolution — each thesis was a proposition offered for formal debate.

The modern doctoral thesis — a book-length original contribution to knowledge — emerged in the nineteenth century. The German Doktorarbeit combined the medieval tradition of defense with the Enlightenment ideal of advancing knowledge. The first PhD in the United States was awarded by Yale in 1861. By the twentieth century, the thesis was the defining requirement of doctoral education: a work that places something new in the field and defends it before examiners.

The word has weakened in casual English. 'My thesis is that...' now introduces any argument, however informal. The Greek word for placing a proposition before an audience and defending it against attack has become a way of saying 'I think.' The placing softened. The defense disappeared.