When we speak of material nature as being governed by laws, it is sufficiently evident that we use the term in a manner somewhat metaphorical. The laws to which man's attention is primarily directed are moral laws; rules laid down for his actions; rules for the conscious actions of a person; rules which, as a matter of possibility, he may obey or may transgress; the latter event being combined, not with an impossibility, but with a penalty. But the Laws of Nature are something different from this; they are rules for that which things are to do and suffer; and this by no consciousness or will of theirs. They are rules describing the mode in which things do act; they are invariably obeyed; their transgression is not punished, it is excluded. The language of a moral law is, man shall not kill; the language of a Law of Nature is, a stone will fall to the earth.

These two kinds of laws direct the actions of persons and of things, by the sort of control of which persons and things are respectively susceptible; so that the metaphor is very simple; but it is proper for us to recollect that it is a metaphor, in order that we may clearly apprehend what is implied in speaking of the Laws of Nature.

In this phrase are included all properties of the portions of the material world; all modes of action and rules of causation, according to which they operate on each other.