Guillaume's theory of psychomechanics views language as systematic and semiotic, with the use of verb forms governed by the meaning we want to express, which is embedded in the unconscious resources of one's native tongue rather than in rules. Through his application of Guillaume's framework Walter Hirtle provides original insights on such topics as the treatment of the progressive and the perfect in English, the use of 'do' as an auxiliary in questions and negations, and tense and its relation to aspect and mood. Hirtle is the former director of the Fonds Gustave Guillaume, an archive of 60,000 manuscript pages of the theorist's work, housed at Laval University, the world centre for the study of psychomechanics.