Halliday & Matthiessen (1999: 258):
Like lexical metaphors, so also grammatical metaphors may become codified in the language and 'take over' as the normal mode of expression. We shall refer below to two instances of this type in English: those like have a look, take a step and those like span, cover, accompany. There are other features of the grammar that are in origin metaphorical (many of the uses of the possessive form, such as [he didn't approve of] my leaving home), but whose origin is so obscured by the natural evolution of the language that all sense of their metaphoric nature has long since been lost.