The reader must naturally have a strong inducement to co-operate with the present author, if he has formed the intention of erecting a complete and solid edifice of metaphysical science, according to the plan now laid before him. Metaphysics, as here represented, is the only science which admits of completion—and with little labour, if it is united, in a short time; so that nothing will be left to future generations except the task of illustrating and applying it _didactically_. For this science is nothing more than the inventory of all that is given us by _pure reason_, systematically arranged. Nothing can escape our notice; for what reason produces from itself cannot lie concealed, but must be brought to the light by reason itself, so soon as we have discovered the common principle of the ideas we seek. The perfect unity of this kind of cognitions, which are based upon pure conceptions, and uninfluenced by any empirical element, or any peculiar intuition leading to determinate experience, renders this completeness not only practicable, but also necessary. Tecum habita, et nôris quam sit tibi curta supellex. —Persius. Satirae iv. 52. Such a system of pure speculative reason I hope to be able to publish under the title of _Metaphysic of Nature_[2]. The content of this work (which will not be half so long) will be very much richer than that of the present Critique, which has to discover the sources of this cognition and expose the conditions of its possibility, and at the same time to clear and level a fit foundation for the scientific edifice. In the present work, I look for the patient hearing and the impartiality of a _judge;_ in the other, for the good-will and assistance of a _co-labourer_. For, however complete the list of _principles_ for this system may be in the Critique, the correctness of the system requires that no _deduced_ conceptions should be absent. These cannot be presented _à priori_, but must be gradually discovered; and, while the _synthesis_ of conceptions has been fully exhausted in the Critique, it is necessary that, in the proposed work, the same should be the case with their _analysis_. But this will be rather an amusement than a labour. [2] In contradistinction to the Metaphysic of Ethics. This work was never published. PREFACE TO THE SECOND EDITION 1787