In 1984, Mark STEEDMAN [7] proposed a generative grammar based on six context sensitive rewriting rules able to produce a large variety of blues chord sequences. Later, François PACHET [6] developed a method for analyzing jazz chord sequences. Then, Marc CHEMILLER [4] [5] uses STEEDMAN's grammar to compose by computers jazz music based upon chord sequences generated by this grammar. About twenty years after his first work, STEEDMAN [8] [9] comes back to chord sequences analysis, but now with the aim of recognition based upon categorial grammars. Meanwhile, pregroup grammars have been conceived as an algebraic tool to recognize well-formed sentences in natural languages [1] [2]. Here we wish to use pregroup grammars to recognize well-formed sequences of chords, especially in Jazz music. Our recognition process reduces the chord sequence to a simpler one. If this later sequence is similar to a well-known pattern like blues, rag, “anatole” or other, we can classify the original sequence as conform to this pattern.