A. Some Sacrament Did Need to be Instituted

224. About the first I say that ‘some sacrament needs to be instituted’ cannot be proved with necessity: not a priori because God does nothing necessarily outside himself; nor a posteriori, or from the end, because an invisible effect could be had without a sacramental sign.

225. But that it was fitting for a sacrament to be instituted is proved by a reason similar to the one set down in the preceding question [nn.190-193], where the possibility of a sacrament was proved.

226. For it is fitting that an invisible effect, ordaining man to salvation and in need of being caused by God, be signified by some sensible thing, so that the wayfarer, acquiring knowledge of it from sensible things, might come to know the invisible effect more certainly.

227. Nor is a fitting sign of this sort of effect only a quasi theoretical one, namely one by which a concept of the thing signified (as ‘man’ signifies human nature) could be got, but a fitting sign is also a quasi practical one, namely one that signifies that the thing signified is or is coming to be.

228. Nor further is a doubtful or equivocal or uncertain practical sign a fitting sign; for although a man might be led by such a sign to knowledge of the coming to be of this sort of effect, yet he would not desire the sign to be applied to himself because of the uncertainty of the sign in respect of the coming to be of the thing signified. Therefore it was fitting for such an effect to be signified by a certain and efficacious practical sign, so that man too might know the effect from such a sign and might more ardently seek after the effect in that sign.

229. But it is not fitting that the sign be certain with the certitude of demonstration, but that it be so as it were for the most part. For just as in theoretical matters there is a sign that is necessary and a sign holding for the most part (from Posterior Analytics 1.30.87b19-25), so could a practical sign have as it were necessary certitude, if it universally and as it were necessarily accompanies the coming to be of the effect, or a certitude for the most part, if it accompanies the effect for the most part.

It is not fitting that a sensible sign be certain in the first way, because since a sensible sign needs to be applied by man, it would follow that there would be in man’s power some sign upon which God would universally cause the invisible effect; and this would take away due preparation from the receiver, since it would be sufficient for him to receive the sign however indisposed he was.

But it is fitting for such invisible effect to be signified by a sensible sign that is certain with certitude for the most part, that is to say always, unless the indisposition of the received prevent it - and this is fittingly signified by a sign naturally preceding the coming to be of the thing signified, so that thus the receiving of the sign would be as it were a disposition for the thing signified.

230. All these conditions of a sign, namely that it be practical, certain for the most part, and naturally preceding the coming to be of the thing signified, I understand to be meant by the term ‘efficacious’. But such a sign cannot be any sensible thing that signifies naturally, because nothing sensible has a natural efficacy for an invisible effect. Therefore it is fitting for the sign to be instituted or imposed.

231. In this way, therefore, one gets (according to the whole idea of a sacrament) that it was fitting for a sacrament to be instituted to cause knowledge and desire in the wayfarer in respect of the invisible effect.

232. And this is one of the ideas of a sacrament that the Master touches on in the text, namely ‘for teaching’. He touches on the other two ideas in the text, namely for ‘exercise and humility’, whose explication he touches on in the text. And these three ideas of a sacrament establish the nature of a sacrament’s institution, on the part of any private person.

233. But there is another idea that touches on fittingness on the part of the whole community. For it is fitting for men of one sect to come together under some exterior signs, by which too they may be distinguished from those of another sect; for by such signs a man knows who is of his sect and who of a different sect. And this is expedient, because those who know themselves to be of the same sect aid each other mutually in the observance of it, and those who know themselves to be of a dissimilar sect mutually avoid each other as mutually impeding each other. Now it is expedient that such a sign, uniting those who are of the same sect and distinguishing them from others, be practical with respect to some visible effect pertaining to observance of the sect.

234. It is plain, therefore, that not necessity [n.224] but fittingness can be proved by reason [nn.225-233].

235. The fact, however, is proved by authority, as will be touched on in the fourth article [n.343], because authorities do not speak of a sacrament taken universally (as it is still being treated here), but speak specifically of such and such a sacrament of such and such a law.