The first requisite for every proof, whether it be derived from the immediate empirical presentation (as in the proof from observation of the object or from experiment) of that which is to be proved, or by Reason _a priori_ from principles, is this. It should not _persuade_, but _convince_,[138] or at least should tend to conviction. _I.e._ the ground of proof or the conclusion should not be merely a subjective (aesthetical) determining ground of assent (mere illusion), but objectively valid and a logical ground of cognition; for otherwise the Understanding is ensnared, but not convinced. Such an illusory proof is that which, perhaps with good intent but yet with wilful concealment of its weaknesses, is adduced in Natural Theology. In this we bring in the great number of indications of the origin of natural things according to the principle of purposes, and take advantage of the merely subjective basis of human Reason, viz. its special propensity to think only one principle instead of several, whenever this can be done without contradiction; and, when in this principle only one or more requisites for determining a concept are furnished, to add in our thought these additional [features] so as to complete the concept of the thing by arbitrarily supplementing it. For, in truth, when we meet with so many products in nature which are to us marks of an intelligent cause, why should we not think One cause rather than many; and in this One, not merely great intelligence, power, etc., but rather Omniscience, and Omnipotence--in a word, think it as a Cause that contains the sufficient ground of such properties in all possible things? Further, why should we not ascribe to this unique, all-powerful, original Being not only intelligence for natural laws and products, but also, as to a moral Cause of the world, supreme, ethical, practical Reason? For by this completion of the concept a sufficient principle is furnished both for insight into nature and for moral wisdom; and no objection grounded in any way can be made against the possibility of such an Idea. If now at the same time the moral motives of the mind are aroused, and a lively interest in the latter is added by the force of eloquence (of which they are indeed very worthy), then there arises therefrom a persuasion of the objective adequacy of the proof; and also (in most cases of its use) a wholesome illusion which quite dispenses with all examination of its logical strictness, and even on the contrary regards this with abhorrence and dislike as if an impious doubt lay at its basis.--Now against this there is indeed nothing to say, so long as we only have regard to its popular usefulness. But then the division of the proof into the two dissimilar parts involved in the argument--belonging to physical and moral Teleology respectively--cannot and must not be prevented. For the blending of these makes it impossible to discern where the proper force of the proof lies, and in what part and how it