In LEXICON 3.3.3, we listed the manual markers of deontic and epistemic modality. Generally speaking, deontic modality conveys obligation, prohibition, necessity, recommendation, ability, permission, intention and volition. On the other hand, epistemic modality refers to the expression of the signer’s judgment or evaluation about the likelihood of the event of the utterance. Signers can express their absolute certainty about the happening or not of an event (either past, present or future) based on their knowledge and evidences, or they can express their evaluations and hypotheses.
LIS encodes deontic and epistemic modality through lexical markers occurring with dedicated non-manuals, which can also spread on the entire sentence. Nevertheless, sometimes lexical signs can be dropped, and modality is encoded through non-manual markers alone. Crucially, the different non-manual markers employed specify the degree of certainty the signer has about his/her proposition. We describe the morphological strategies for deontic and epistemic modality, respectively, in the following sections.