Modalization operates on propositions, in the space between ‘It is…‘ and ‘It isn’t…‘. There are “two kinds of intermediate possibilities: (i) degrees of probability [and] (ii) degrees of usuality” (H & M, p.147). Probability is concerned with “‘either yes or no’, that is, maybe yes, maybe no, with different degrees of likelihood attached. This degree of likelihood may be construed as being either subjective or objective.
Here is a quote from Bill O’Reilly, cited on Huffington Post:
I may be an idiot.
This expresses a Low subjective opinion that implicitly admits to the possibility of it being true. We can change this, of course, to High:
I must be an idiot.
We have, then, three values of implicit subjective probability:
High: She must know.
Medium: She’ll know.
Low: She may know.
We can also make the Medium and Low values softer by creating metaphorical distance through the past tense: She’ll know → She’d know and She may know → She might know.
We can also, however, make this subjective opinion more explicit with grammatical metaphor. Here, being concerned with opinions and statements, we most commonly use mental Processes:
High: I know she knows.
Medium: I think she knows.
Low: I guess she knows.
Here is an overheard conversation that was reported in Column 8:
Lady: How much is this metal hat stand?
Vendor: $260. It’s Victorian.
Lady: Well you must mean it comes from Melbourne, because it’s certainly not that old.
After subjective hedging to imply ‘it’s just my opinion’ (you must mean), the speaker offers an objective assessment regarding the age of the hat stand (it’s certainly not that old) that is also construed as being ‘obvious’, or implicit. Again, we can have three values:
High: She certainly knows.
Medium: She probably knows.
Low: She possibly knows.
We can also construe it as being an explicit objective opinion, metaphorically separate from the speaker:
High: It’s certain that she knows.
Medium: It’s probable that she knows.
Low: It’s possible that she knows.