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