The passage illustrates disagreement by referring to claims made in different theological and philosophical schools. Some Muʿtazilites regarded human authorship of acts as obvious; some philosophers regarded preference between alternatives without a determining factor as impossible; Ashʿarite disputants contested certain such claims.
These examples report rival assertions of obviousness, not full proofs of each school’s position. The point is that one party's labeling a disputed doctrine as self-evident does not settle the matter for another party.
If a judgment contains technical terms, hidden premises or distinct respects, these must be clarified. A complex theoretical dispute is not resolved simply by declaring one side's conclusion “plainly evident.”