Page "Origin of language" Paragraph 49

In order to reconstruct the evolutionary transition from early language to languages with complex grammars, we need to know which hypothetical sequences are plausible and which are not.

In order to convey abstract ideas, the first recourse of speakers is to fall back on immediately recognisable concrete imagery, very often deploying metaphors rooted in shared bodily experience.

A familiar example is the use of concrete terms such as ' belly ' or ' back ' to convey abstract meanings such as ' inside ' or ' behind '.

Equally metaphorical is the strategy of representing temporal patterns on the model of spatial ones.

Hence in English we say ' It is going to rain ', modelled on ' I am going to London '.

We might abbreviate this colloquially to ' It's gonna rain '.

Even when in a hurry, we don't say ' I'm gonna London ' – the contraction is restricted to the job of specifying tense.

From such examples we can see why grammaticalisation is consistently unidirectional – from concrete to abstract meaning, not the other way around.