 In 1929, with "Temps et Verbe", he described how the systems of aspect, mood and tense operate to produce an image of time proper to the event that is expressed by a verb in a sentence.This breakthrough gave him a first view of the mental system – the "psychosystem", as he later called it – of the verb and led him to realize that, as a part of speech, the verb is a system of systems that the speaker can use to construct a verb each time it is needed during the give-and-take of ordinary speech.From that point on in his career, he tried to analyze how words of different types are constructed – attempting to identify the grammatical systems involved in configuring a word's lexical importance, giving rise to the parts of speech observed in French and other 
Indo-European languages.