Change is not, however, the only instance of the principle of Ground and Consequence. These two aspects may also be found in systematic wholes which contain no element of succession in time, _e.g._ in a body of logical deductions from a few fundamental premisses. The special peculiarity of the case of Change is that it is the principle of Ground and Consequence as applied to a material which is successive _in time_. As thus applied, the principle has received the special name of the _Principle of Sufficient Reason_, and may be formulated thus: _Nothing takes place unless there is a sufficient reason why it should occur rather than not_. It is clear that such a proposition is a mere result of the application of the conception of Reality as a systematic whole to the special case of the existence of the successive in time. It is therefore simply one case of the fundamental axiom of all knowledge, the axiom that what truly exists is a coherent whole.[103] We must of course observe that the principle does nothing to solve the perhaps insoluble problem _why_ succession in time should be a feature of experience. This is a question which could only be answered if we could show that succession in time is a logical consequence of the existence of any multiplicity forming a systematic whole. Until we are able to establish this result, we have simply to accept succession as a datum of our experience. (Yet for some light upon the problem, see _infra_, Bk. III chap. 4, § 9) § 4. _Causality._ So far we have said nothing of a concept which is much more familiar in the popular treatment of the problem of Change than that of Ground and Consequence, the concept of _Cause_. In proceeding to discuss this concept, it is necessary in the first place to explain which of the numerous senses of the word we are taking for examination. There was an old scholastic distinction, which still reappears occasionally in philosophical writings, between the _Causa cognoscendi_, or reason for affirming a truth, and the _Causa existendi_ or _fiendi_, the cause of the occurrence of an event. It is this latter meaning of the word “cause,” the meaning which is predominant wherever the term is used in modern scientific language, that we shall have in view in the following sections.