Supposition theory was a branch of medieval logic that was probably aimed at giving accounts of issues similar to modern accounts of reference, plurality, tense, and modality, within an Aristotelian context. Philosophers such as John Buridan, William of Ockham, William of Sherwood, Walter Burley, and Peter of Spain were its principal developers. By the 14th century it seems to have drifted into at least two fairly distinct theories, the theory of "supposition proper" which included an "ampliation" and is much like a theory of reference, and the theory of "modes of supposition" whose intended function is not clear.