is no essential or natural reason why a particular signifier should be attached to a particular signified. Saussure calls this the "arbitrariness of the sign" (l'arbitraire du signe). No two people have precisely the same concept of "tree," since no two people have precisely the same experiences or psychology. We can communicate "tree," however, for the same reason we can communicate at all: because we have agreed to use it in a consistent way. If we agreed to use the word and sound for "horse" instead, it would be called "horse" to the same effect. Since all that is important is agreement and consistency, the connection is arbitrary. In further support of the arbitrary nature of the sign, Saussure goes on to argue that if words stood for pre-existing universal concepts they would have exact equivalents in meaning from one language to the next and this is not so. Languages reflect shared experience in complicated ways and can paint very different pictures of the world from one another. To explain this, Saussure uses the word bœuf as an example. In English, he says, we have different words for the animal and the meat product: Ox and beef. In French, bœuf is used to refer to both concepts. In Saussure's view, particular words are born out of a particular society's needs, rather than out of a need to label a pre-existing set of concepts. But the picture is actually even more complicated, through the integral notion of 'relative motivation'. Relative motivation refers to the compositionality of the linguistic system, along the lines of an immediate constituent analysis. This is to say that, at the level of langue, hierarchically nested signifiers have relatively determined signified. An obvious example is in the English number system: That is, though twenty and two might be arbitrary representations of a numerical concept, twenty-two, twenty-three etc. are constrained by those more arbitrary meanings. The tense of verbs provides another obvious example: The meaning of "kicked" is relatively motivated by the meanings of "kick-" and "-ed". But, most simply, this captures the insight that the value of a syntagm—a system-level sentence—is a function of the value of the signs occurring in it. It is for this reason that Leonard Bloomfield called the lexicon the set of fundamental irregularities of the language. (Note how much of the "meaningfulness" of the Jabberwocky poem is due to these sorts of compositional