Metaphorical Realisation Of Probability

Halliday & Matthiessen (2004: 615-6):

What happens is that, in order to state explicitly that the probability is subjective, or alternatively, at the other end, to claim explicitly that the probability is objective, the speaker construes the proposition as a projection and encodes the subjectivity (I think), or the objectivity (it is likely), in a projecting clause.  (There are other forms intermediate between the explicit and implicit: subjective in my opinion, objective in all probability, where the modality is expressed as a prepositional phrase, which is a kind of halfway house between clausal and non-clausal status.)