An analysis of the modal particle in Homer based on the instances of the root *wekw "speak"

According to the standard Greek grammars, the use of the MP ἄν is governed by the following strict rules in Classical Greek prose: it is mandatory in the main clause and any other subordinate clause (except the conditionals) with a potential optative, an irrealis indicative and an iterative indicative and forbidden with the same forms in a conditional clause (exceptions are attested, but generally corrected by the different editors); it is mandatory with a subjunctive in any subordinate clause, except in the purpose clauses (where it can appear) and clauses after verba timendi (where it never appears); it is forbidden with a future indicative and a subjunctive in the main clause (instances of these uses are attested, but they are generally to be corrected by the editors). In Homeric Greek, not only ἄν is used as MP, but also κεν; moreover, a future indicative and a subjunctive in the main clause can be used with an MP as well and so can optatives in conditional clauses and, inversely, the MP can also be left out. The differences between the presence and absence of the MP have not been conclusively explained.