Halliday & Matthiessen (1999: 242):
The phenomenon of transcategorising elements would seem to be a feature of the grammar of every language. This implies two things:
(i) that each etymon belongs inherently to a major class;(ii) that at least some etymons can be transferred to another class — by some grammatical means, syntactic and/or morphological.
Thus in Indo-European languages there is typically a battery of derivational morphemes whereby a root can be transcategorised; for example in English,All these are means of shifting a lexeme from one class to another.
