Halliday & Matthiessen (2014: 718):
… ideational metaphor also realigns the ideational in relation to the interpersonal. When a sequence is realised metaphorically by a clause, it is given the interpersonal status of a proposition or proposal, making it arguable. For example:
||| Too many unprogrammed deployments will inevitably disrupt operating budgets, || sap morale, || cause lost training opportunities, || and accelerate wear and tear on equipment. |||
||| A magnitude-6 quake can cause severe damage || if it is centred under a populated area. |||
||| This is consistent with the concept [[ that the antarctic ozone hole phenomenon causes a dilution effect throughout much of the Southern Hemisphere]] . |||
As the examples illustrate, a ‘propositionalised’ sequence can be modalised, doubted, argued and negotiated interpersonally in numerous other ways.