No one will claim that either of these is the sense in which the word is used in reference to the nature of the mind of man as a race.
The leading and primary signification of the word _nature_ is that which is intended and understood when we say that "the _nature_ of a design or construction is proof of the character and intention of the author." It is in this sense that men use the word when they speak of the nature of animals, the nature of trees, and the nature of the soul.
In this use, it has but one signification, and that is, _those qualities, powers and faculties which are discovered by experience and observation_. Or in other words, when we discover the qualities of a thing, how it acts, and how it is acted upon, we learn its _nature_.
In regard to all other existences except mind, the only mode of discovering _their nature_ is to ascertain by experience and observation how they _invariably_ appear and act. Thus we decide that it is the nature of water to run down hill by finding that it _invariably_ does so; and that it is the nature of smoke to rise in the atmosphere by observing that it _invariably_ ascends.
Owing to this, mankind often use the word _nature_ as signifying _that which is according to ordinary experience_. That is to say, the same word is used to express the _qualities and powers_ of things, and also to express that _invariable experience_ by which we learn these qualities and powers. What is according to our ordinary experience we say is according to nature, and what is contrary to ordinary experience is contrary to nature.
Thus it is according to nature for water to run down hill, and it is contrary to nature for it to run up hill.
It is mind, in distinction from matter, which has the power of _willing_, and this is a power which never is exercised _invariably_ one way or another.
But theologians have practiced this fallacy on themselves and others. They first assume, what is contrary to fact, that mind _invariably_ chooses one way, and that is _wrong_, from birth to regeneration. This being assumed without proof, they claim that the _nature_ of the human mind is thus proved to be depraved, and totally so.
Having thus, as they imagine, established its depraved voluntary nature, they claim that, like all other things, the mind _must act according to its nature_, which, being wholly depraved, all its moral acts are consequently depraved.