Saussure argues that syntagmatic relations are more like multiplication than addition. Adding - eux to desir is not putting together “independent units”; rather the two “form a product, a combination of interdependent elements, their value deriving solely from their mutual contributions within a higher unit.”

At another level, we can say the same about sentences: Words are not added up in a sentence, but the sentence is the product of something more like multiplication, the product of the interdependent elements of the sentence.