Construing Perceptual Meaning As Linguistic Meaning

Halliday & Matthiessen (1999: 512-3):

Suppose we are standing on the shore, and there is a rapid movement across our line of vision. We construe this grammatically as

birds + are flying + across the sea

This is obviously not the only way such an experience could be "semanticised": it might be construed as a single unanalysed phenomenon, e.g. it's winging. Some processes are in fact construed in this way: in English, for example, meteorological processes such as it's raining. But in most instances the theory propounded by the grammar is that this is a composite phenomenon, an organic construction of functionally distinct parts: here, a process are flying, something participating in this process, namely birds, and a relevant circumstance across the sea. This allows for other things to fly across the sea, such as insects and aeroplanes; for birds to fly in other locations, such as over the trees, and to do other things than flying, such as singing or quarrelling. The meaning potential here is clearly far greater than if a different lexical item was used to construe every possible configuration.