We say, "_trees grow_." But suppose no change had ever been observed in trees, that they had always been as they now are; in stature as lofty, in foliage as green and beautiful, in location unaltered. Who would then say, "trees grow?"
In this single expression a whole train of facts are taken into the account, tho not particularly marked. As a single expression we imply that _trees increase their stature_. But this we all know could never be effected without the influence of other causes. The soil where it stands must contain properties suited to the _growth_ of the tree. A due portion of moisture and heat are also requisite. These facts all exist, and are indispensable to make good the expression that the "tree grows." We might also trace the capabilities of the tree itself, its roots, bark, veins or pores, fibres or grains, its succulent and absorbent powers. But, as in the case of the "man that killed the deer," noticed in a former lecture, the mind here conceives a single idea of a complete whole, which is signified by the single expression, "trees grow."
Let the following example serve in further illustration of this point. Take two bricks, the one heated to a high temperature, the other cold. Put them together, and in a short time you will find them of equal temperature. One has grown warm, the other cool. One has _imparted_ heat and _received_ cold, the other has _received_ heat and _imparted_ cold. Yet all this would remain forever unknown, but for the effects which must appear obvious to all. From these effects the causes are to be learned.
It must, I think, appear plain to all who are willing to see, that action, as such, can never exist distinct from the thing that acts; that all our notions of action are derived from an observance of _things_ in an acting condition; and hence that no words can be framed to express our ideas of action on any other principle.
I hope you will bear these principles in mind. They are vastly important in the construction of language, as will appear when we come to speak of the _agents_ and _objects_ of action. We still adhere to the fact, that no rules of language can be successfully employed, which deviate from the permanent laws which operate in the regulation of matter and mind; a fact which can not be too deeply impressed on your minds.