Probability Realised By Both Finite Modal Operator And Noun Of Modalisation

There are thus 2 probabilities:

1. the probability of complications or adverse effects (➘ noun of modalisation);
2. the probability of increasing that probability (➘ Finite).

For nouns of modalisation, see Halliday & Matthiessen (2014: 536).

'Dare' As Finite vs Event

The unmarked Mood tag of the first clause is dare they?

The unmarked Mood tag of the second clause is would they?

See Halliday & Matthiessen (2014: 574): 'risk doing', 'venture to do'.

'Must' & 'Have To': Obligation & Probability

Both 'must' and 'have to' can realise high value obligation or probability, the latter form evolving from an earlier conative function; see Halliday & Matthiessen (2014: 145, 572-3, 583).

 modulation: obligation (high value)

she	must	go
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

she	has	to go
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

modalisation: probability (high value)

she	must	have gone
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue

she	has	to have gone
Theme	Rheme
Actor	Process: material
Subject	Finite	Predicator
Mood		Residue