Linguistic modality includes necessity and possibility (Psbl), each with a situational (objective, fact-based) and an epistemic (subjective, speaker-specific) variant. Situational possibility may refer to one of three options: (a) ability or skill (as in She can swim), (b) permission (as in She is allowed to swim), and (c) objectively possible option (as in This is a lake one can swim in). This parameter considers the use of grammatical, rather than lexical, strategies for conveying situational possibility. These strategies — which may serve multiple functions in addition to expressing situational possibility — include verbal affixes, verbal constructions (including auxiliaries and serial verb constructions), and other markers, such as particles, adverbials, nouns, adjectives, and complex sentence structures.
NonSitPsbl: No grammatical strategies exist to express situational possibility.
SitPsblAff: Situational possibility is expressed through the use of verbal affixes. 
SitPsblV: Situational possibility is expressed through the use of verb constructions.
SitPsblNonaffNonV: Situational possibility is expressed through a strategy other than verbal affixes and verb constructions.
When a language displays more than one strategy, multiple values can be listed. If one strategy is dominant, a slash (/) can separate the two values, with the dominant value appearing first; if neither is dominant, they are listed with an ampersand (&) separating the two.
 Example of epistemic possibility: She could be home now (= I think it’s possible she is home now). Epistemic necessity: She should be home by now (= I’m nearly certain she’s home now). Situational necessity: One needs to breathe to stay alive.
 This value applies even if the use of verb affixes is not the only strategy available in the language for the expression of situational possibility.
 This should be detailed in the commentary.