Kant

“The empiricist will never allow himself to accept any epoch of nature for the first–the absolutely primal state; he will not believe that there can be limits to his outlook into her wide domains, nor pass from the objects of nature, which he can satisfactorily explain by means of observation and mathematical thought–which he can
determine synthetically in intuition, to those which neither sense nor imagination can ever present in concreto; he will not concede the existence of a faculty in nature, operating independently of the laws of nature–a concession which would introduce uncertainty into the procedure of the understanding, which is guided by necessary laws to the observation of phenomena; nor, finally, will he permit himself to seek a cause beyond nature, inasmuch as we know nothing but it, and from it alone receive an objective basis for all our conceptions and instruction in the unvarying laws of things.

In truth, if the empirical philosopher had no other purpose in the establishment of his antithesis than to check the presumption of a reason which mistakes its true destination, which boasts of its insight and its knowledge, just where all insight and knowledge cease to exist, and regards that which is valid only in relation to a practical interest, as an advancement of the speculative interests of the mind (in order, when it is convenient for itself, to break the thread of our physical investigations, and, under pretence of extending our cognition, connect them with transcendental ideas, by
means of which we really know only that we know nothing)–if, I say, the empiricist rested satisfied with this benefit, the principle advanced by him would be a maxim recommending moderation in the pretensions of reason and modesty in its affirmations, and at the same time would direct us to the right mode of extending the province of the understanding, by the help of the only true teacher, experience.

In obedience to this advice, intellectual hypotheses and faith would not be called in aid of our practical interests; nor should we introduce them under the pompous titles of science and insight. For speculative cognition cannot find an objective basis any other where than in experience; and, when we overstep its limits our synthesis, which requires ever new cognitions independent of experience, has no substratum of intuition upon which to build.

But if–as often happens–empiricism, in relation to ideas,
becomes itself dogmatic and boldly denies that which is above the sphere of its phenomenal cognition, it falls itself into the error of intemperance–an error which is here all the more reprehensible, as thereby the practical interest of reason receives an irreparable injury.

And this constitutes the opposition between Epicureanism and Platonism.”