The communication systems of songbirds is commonly described as a system that is based on syntactic operations. Specifically, bird song enables the systematic combination of sound elements in order to string together a song. Likewise, human languages also operate syntactically through the combination of words, which are calculated systematically. While the mechanics of bird song thrives off of syntax, it appears as though the notes, syllables, and motifs that are combined in order to elicit the different songs may not necessarily contain any meaning. The communication system of songbirds’ also lacks a lexicon that contains a set of any sort of meaning-to-referent pairs. Essentially, this means that an individual sound produced by a songbird does not have meaning associated with it, the way a word does in human language. Bird song is capable of being structured, but it is not capable of carrying meaning. In this way, the prominence of syntax and the absence of lexical meaning presents bird song as a strong candidate for being a simplified antecedent of the E component that is found in human language, as this component also lacks lexical information. While birds that use bird song can rely on just this E component to communicate, human utterances require lexical meaning in addition to structural operations a part of the E component, as human language is unable to operate with just syntactic structure or structural function words alone. This is evident as human communication does in fact consist of a lexicon, and humans produce combined sequences of words that are meaningful, best known as sentences. This suggests that part of human language must have been adapted from another animal's communication system in order for the L component to arise .