A reason sentence describe two events whose relationship answers the question ‘Why?’ Two types of structures are possible: (a) a verb or nonfinite verb form, with or without arguments or adjuncts; (b) a reason clause (RC) containing a finite verb. This parameter considers the form in which the verb appears in a reason clause. Specifically, the verb of the reason clause is examined and compared to that of an independent declarative (non-reason) clause.  If the two verb forms are identical, the RC verb form is considered “balanced.” If they differ, the RC verb appears in a special form, also known as “deranked” or “demoted.” Although most languages display one type rather than the other, some may display both types, with or without grammatical restriction on their use.
CauseVBal: The verb of a reason clause obligatorily appears in base form.
CauseVBalDiffV: The verb of a reason clause appears in either base form or a special form, depending on grammatical features of the verb, such as transitivity and aspect.
CauseVDrk: The verb of a reason clause obligatorily appears in a single special form, regardless of its grammatical features.
CauseVDrkDiffV: The verb in a reason clause appears, or can appear, in different special forms, depending on the grammatical features of the verb.
+DrkSameSbj: The verb of the reason clause can only appear in a special form when the subject of the two clauses is the same.
When a language displays more than one type, multiple values can be listed. The value +DrkSameSbj can only appear in conjunction with another value, with the exception of CauseVBal. If one type 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. The use of parentheses indicates that use of the strategy is not obligatory.
 If the difference between the reason clause and the independent verb form is that the reason clause has a special affix or clitic, and its removal would result in the form used in an independent clause, then the two verb forms are considered to be the same, since the affix functions as a conjunction marking the structure as a reason clause.
 Special or “demoted/deranked” verb forms are originally derived from a verb but now function as a different word class. Examples include gerunds, converbs, and participles. Special verb forms also include finite verbs that differ from the base form in their marking of person, case, mood, or aspect or in their co-occurrence with adpositions. These verb forms may also fulfill other functions in the language, in addition to their role in reason clauses.
 The commentary should specify whether use is obligatory or optional.
 This includes sentences in which the causal relationship between the two events can only be determined by contextual or pragmatic clues.
 “Appears” refers to obligatory use, whereas “can appear” refers to the optional (or partially optional) use of distinct special forms. Although the parameter value applies equally to both types, it should be specified in the commentary whether use is obligatory or optional.
 In languages of this type, a sentence such as “The prisoner went free, because he was deemed innocent” can be formed with the use of a special verb form, while a sentence such as “The prison guards let the prisoner go, because he was found innocent” cannot.