Reversible sentences are those in which the permutation of the two arguments changes the meaning of the sentence by inverting the attribution of the semantic roles. For example, the sentence ‘The woman combs the child’, can be can be changed into the sentence ‘The child combs the woman’ through the permutation of the two noun phrases.
Irreversible sentences are those in which permutation is not possible due to the meaning of the predicate and/or the arguments. For example, in the sentence ‘The man touches the mountain’ such permutation is not possible due to the inanimate feature of the object ‘mountain’; while in the sentence ‘The man cooks the egg’ the permutation of the sentence arguments is blocked by the semantics of the English verb ‘cook’ which typically implies a human subject and a non-human object.
If the predicate is reversible, namely the two characters can perform the action on each other, word order may be the only clue to understand who is the agent and who is the theme. If the predicate is irreversible, word order is less crucial in determining the role of the arguments in the sentence.
While the SVO order is preferred in LIS in reversible sentences displaying plain verbs, the SOV order is preferred with irreversible predicates, or with reversible predicates when verbal inflection, the use of space and the use of classifiers, clarifies the syntactic roles of the predicate arguments. An example of a sentence displaying an irreversible verb is provided in (a), while (b) illustrates an example of a reversible sentence displaying the SVO order.
a. woman meat eat
‘The woman eats the meat.’
b. doga abiteb catb
‘The dog bites the cat.’