The highest formal unity, which is based upon ideas alone, is the unity of all things- a unity in accordance with an aim or purpose; and the speculative interest of reason renders it necessary to regard all order in the world as if it originated from the intention and design of a supreme reason.This principle unfolds to the view of reason in the sphere of experience new and enlarged prospects, and invites it to connect the phenomena of the world according to teleological laws, and in this way to attain to the highest possible degree of systematic unity.The hypothesis of a supreme intelligence, as the sole cause of the universe- an intelligence which has for us no more than an ideal existence- is accordingly always of the greatest service to reason.Thus, if we presuppose, in relation to the figure of the earth (which is round, but somewhat flattened at the poles),* or that of mountains or seas, wise designs on the part of an author of the universe, we cannot fail to make, by the light of this supposition, a great number of interesting discoveries.If we keep to this hypothesis, as a principle which is purely regulative, even error cannot be very detrimental.For, in this case, error can have no more serious consequences than that, where we expected to discover a teleological connection (nexus finalis), only a mechanical or physical connection appears.In such a case, we merely fail to find the additional form of unity we expected, but we do not lose the rational unity which the mind requires in its procedure in experience.But even a miscarriage of this sort cannot affect the law in its general and teleological relations.For although we may convict an anatomist of an error, when he connects the limb of some animal with a certain purpose, it is quite impossible to prove in a single case that any arrangement of nature, be it what it may, is entirely without aim or design.And thus medical physiology, by the aid of a principle presented to it by pure reason, extends its very limited empirical knowledge of the purposes of the different parts of an organized body so far that it may be asserted with the utmost confidence, and with the approbation of all reflecting men, that every organ or bodily part of an animal has its use and answers a certain design.Now, this is a supposition which, if regarded as of a constitutive character, goes much farther than any experience or observation of ours can justify.Hence it is evident that it is nothing more than a regulative principle of reason, which aims at the highest degree of systematic unity, by the aid of the idea of a causality according to design in a supreme cause- a cause which it regards as the highest intelligence.
*The advantages which a circular form, in the case of the earth, has over every other, are well known.But few are aware that the slight flattening at the poles, which gives it the figure of a spheroid, is the only cause which prevents the elevations of continents or even of mountains, perhaps thrown up by some internal convulsion, from continually altering the position of the axis of the earth- and that to some considerable degree in a short time.The great protuberance of the earth under the Equator serves to overbalance the impetus of all other masses of earth, and thus to preserve the axis of the earth, so far as we can observe, in its present position.And yet this wise arrangement has been unthinkingly explained from the equilibrium of the formerly fluid mass.
If, however, we neglect this restriction of the idea to a purely regulative influence, reason is betrayed into numerous errors.For it has then left the ground of experience, in which alone are to be found the criteria of truth, and has ventured into the region of the incomprehensible and unsearchable, on the heights of which it loses its power and collectedness, because it has completely severed its connection with experience.