Subjective modality shares with illocution the property of regarding the speaker's attitude or assessment concerning his proposition. The basic difference between them is that the latter concerns the relation between the speaker and the hearer – thus the goals and operations of communication –, whereas the former does not. In other words:

• Modality is a binary relation between an entity that is the source of the modality and the proposition or situation conveyed. It belongs to the cognitive domain of language. To the extent it is grammaticalized, it produces modal grammatical categories.
• Illocution is a ternary relation between the speaker, the hearer and the proposition conveyed. It belongs to the communicative domain of language. To the extent that illocution is grammaticalized, it constitutes sentence types.

The hierarchical relation between the two categorizations is as follows:

• Illocution is the uppermost categorization of propositions. It does not, in effect, categorize propositions, but instead uses of a proposition, thus, utterances.
• Within each of the sentence types constituted by an illocution, there may be a paradigm of modal distinctions. Some modal distinctions may cross-cut sentence types; others may be restricted to a certain sentence-type. Yet other sentence types may not allow any modal distinctions.

Methodologically, this entails the following: If some semantic category/relation appears to be a modality, but does not function within any of the independently established sentence types, then it is, instead, a sentence type of itself.

Thus, the optative modality marked both by Latin utinam in and by may in the English translation is not really a modality and instead an illocutionary force, since there is no paradigm of sentence types for it; i.e. the content of , including the optative modality, cannot be questioned or ordered by transforming the sentence into an interrogative or imperative sentence.

More on sentence types elsewhere.