Semantics is the study of meaning in language, i.e., the study of the relationship between linguistic expressions and reality. This should be compared to syntactics, which is only concerned with the form of expressions in a language. The difference between syntactic and semantic properties of language is illustrated in the following example. Consider the sentence: "Colourless green ideas sleep furiously". From a syntactic point of view, this sentence is perfectly correct. It contains the subject "Colourless green ideas" and the predicate "sleep furiously". Semantically, however, the sentence is quite absurd since it does not describe any conceivable state of affairs. The adjective "colourless" indicates the property "without colour", but it is combined with the adjective "green", which bestows the property "green in colour". This is unreasonable since something cannot be both green and without colour at the same time. Several other semantic violations also occur in the sentence, making it an example of a syntactically correct but meaningless sentence. It is instructive to compare the sentence with a syntactically incorrect sentence such as "Sleep colourless furiously green ideas". This sentence contains the same words as the previous one but in an order that makes it syntactically incorrect. It lacks sufficient structure to make it possible to say what is wrong with it.