The Classifier indicates a particular subclass of the thing in question, e.g. 'electric trains', 'passenger trains', 'wooden trains', 'toy trains'. Sometimes the same word may function either as Epithet or as Classifier with a difference in meaning : e.g. 'fast trains' may mean either ʻtrains that go fastʼ (fast = Epithet) or ʻtrains classified as expressesʼ (fast = Classifier). The line between Epithet and Classifier is not a very sharp one, but there are significant differences. Classifiers do not accept degrees of comparison or intensity – we cannot have 'a more electric train' or 'a very electric train'; and they tend to be organized in mutually exclusive and exhaustive sets – 'a train' is either 'electric', 'steam' or 'diesel'. The range of semantic relations that may be embodied in a set of items functioning as Classifiers is very broad: it includes material, scale and scope, purpose and function, status and rank, origin, made of operation – more or less any feature that may serve to classify a set of things into a system of smaller sets.
- Halliday (1985), a pag.164