This should be done not only when he formulates an objection, but also if, without so doing, he refuses to admit the point because he foresees something of the kind; for if the point objected to is withdrawn, he will be forced to admit the proposition because he cannot foresee in the rest of it any case where it does not hold true: if he refuses to admit it, then when asked for an objection he certainly will be unable to render one.