Or perhaps his mind is not clear, i.e., he cannot achieve full and clear understanding, and yet he is always of one mind. In other words, a deaf-mute functions at the same level of intellectual capacity every day. Rav Ashi explains the other possibility: Or perhaps it is obvious to R' Elazar that the mind of a deaf-mute is weak and his mind is unclear, but in this case here, this is R' Elazar’s reasoning: Since he is at times competent and at times imbecilic, without clarity of mind, i.e., he does not function at the same level of understanding every day, therefore the teruma of a deaf-mute is considered teruma that is of doubtful legal status.
למאי נפקא מינה — להוציא אשתו בגט. אי אמרת חדא דעתא הוא — כקדושין כך גירושין.
The Talmud asks: What is the practical difference how one defines the intellectual capacity of a deaf-mute? The Talmud answers: It makes a difference with respect to divorcing his wife with a bill of divorce. If you say that a deaf-mute has one consistent mind, his divorce is equivalent in status to his betrothal. Since he had a weak mind at the time of his betrothal, he has the same level of competence at his divorce and therefore he may divorce his wife.
But if you say that he is at times competent and at times imbecilic, he may betroth a woman, as the rabbis are stringent and assume that he was healthy and of clear mind at the time; however he cannot divorce her, due to a concern that he was competent when he betrothed her but he is incompetent now. If so, what is R' Elazar’s reasoning? No solution is found, and therefore the Talmud states that the dilemma should stand unresolved.