This distinction may profitably be carried further and emphasized in our terminology. Take any thing, or any integrated group of things, regarded as that higher order of thing which we call a self-contained system. Process occurs therein, and process involves change. In so far as the system is self-contained its changes and states are inherent in its constitution. We need a term by which to designate that which is thus inherent and constitutional. The term _ground_ might be reserved for this purpose. The word ground has its natural home in logic. It is here extended (if it be an extension) to that to which the logic has reference in the existing world. One is here following Spencer, who claims[47] that 'Logic is a science pertaining to objective existence'. On these terms the constitution of any system is the ground of the properties, states, and happenings in that system regarded as isolated. But the changes or properties will be also in relation to surrounding things or systems. _These_ changes, or modifications of change, in relation to external things or events, may properly be said to be conditioned; and we may well restrict the term conditions to influences _outside_ the constitution as ground. Of course, if we accept this usage, we must not speak, with Mill, of the constitution of any system as the condition of its inherent changes or properties. That is why we need some such word and concept as ground. Now we may fix our attention on any constituent part of some natural system and make that part the centre of our interest. That part may be changing in virtue of its constitution; and the rest of the system, regarded as external to this selected part, must therefore be regarded as conditioning. It is a matter of convenience for purposes of scientific interpretation whether we select a larger or a smaller system-group and discuss its constitutional character. Thus we may think of the constitution of the solar system, or of that of the sun's corona; of the constitution of an organism or of that of one of its cells; of the constitution of a complex molecule or of that of an atom therein. We have here reached, or nearly reached, the limiting case in one direction--that of restricting our field of inquiry. The limiting case in the other direction is, I suppose, the universe. But could we so expand our thought as to embrace, if that were possible, the whole universe, then there are no conditions; for _ex hypothesi_ there is nothing for science outside the universe. We have reached the limiting concept. Hence, for science, the constitution of nature is the ultimate ground of all that is or happens. Let us now see how we stand. Consider the following statements: 1. The Unknowable is the cause of all the phenomena we observe. 2. The constitution of gunpowder is the cause of its explosiveness.[48] 3. The fall of a spark was the cause of the actual explosion of the powder.[49] Or these: 1. Life is the cause of all vital manifestations.