In spite of the weight of such recommendations, I find that the second of these two laws has been far too rarely applied to a fundamental principle of all knowledge: _the Principle of Sufficient Reason_. For although this principle has been often and long ago stated in a general way, still sufficient distinction has not been made between its extremely different applications, in each of which it acquires a new meaning; its origin in various mental faculties thus becoming evident. If we compare Kant's philosophy with all preceding systems, we perceive that, precisely in the observation of our mental faculties, many persistent errors have been caused by applying the principle of homogeneity, while the opposite principle of specification was neglected; whereas the law of specification has led to the greatest and most important results. I therefore crave permission to quote a passage from Kant, in which the application of the law of specification to the sources of our knowledge is especially recommended; for it gives countenance to my present endeavour:-- "It is of the highest importance to _isolate_ various sorts of knowledge, which in kind and origin are different from others, and to take great care lest they be mixed up with those others with which, for practical purposes, they are generally united. What is done by the chemist in the analysis of substances, and by the mathematician in pure mathematics, is far more incumbent on the philosopher, in order to enable him to define clearly the part which, in the promiscuous employment of the understanding, belongs to a special kind of knowledge, as well as its peculiar value and influence."[12] [12] Kant, "Krit. d. r. V. Methodenlehre. Drittes Hauptstück," p. 842 of the 1st edition. Engl. Tr. by F. M. Müller. "Architectonic of Pure Reason," p. 723. § 3. _Utility of this Inquiry._