True notions concerning the nature and extent of liberty are of so great importance, that I hope I shall be pardoned this digression, which my attempt to explain it has led me into.  The ideas of will, volition, liberty, and necessity, in this Chapter of Power, came naturally in my way.  In a former edition of this Treatise I gave an account of my thoughts concerning them, according to the light I then had.  And now, as a lover of truth, and not a worshipper of my own doctrines, I own some change of my opinion; which I think I have discovered ground for.  In what I first writ, I with an unbiassed indifferency followed truth, whither I thought she led me.  But neither being so vain as to fancy infallibility, nor so disingenuous as to dissemble my mistakes for fear of blemishing my reputation, I have, with the same sincere design for truth only, not been ashamed to publish what a severer inquiry has suggested.  It is not impossible but that some may think my former notions right; and some (as I have already found) these latter; and some neither.  I shall not at all wonder at this variety in men’s opinions:  impartial deductions of reason in controverted points being so rare, and exact ones in abstract notions not so very easy especially if of any length.  And, therefore, I should think myself not a little beholden to any one, who would, upon these or any other grounds, fairly clear this subject of liberty from any difficulties that may yet remain.

75.  Summary of our Original ideas.

And thus I have, in a short draught, given a view of our original ideas, from whence all the rest are derived, and of which they are made up; which, if I would consider as a philosopher, and examine on what causes they depend, and of what they are made, I believe they all might be reduced to these very few primary and original ones, viz.  extension, solidity, mobility, or the power of being moved; which by our senses we receive from body:  Perceptivity, or the power of perception, or thinking; motivity, or the power of moving:  which by reflection we receive from our minds.

I crave leave to make use of these two new words, to avoid the danger of being mistaken in the use of those which are equivocal.

To which if we add existence, duration, number, which belong both to the one and the other, we have, perhaps, all the original ideas on which the rest depend.  For by these, I imagine, might be explained the nature of colours, sounds, tastes, smells, and all other ideas we have, if we had but faculties acute enough to perceive the severally modified extensions and motions of these minute bodies, which produce those several sensations in us.  But my present purpose being only to inquire into the knowledge the mind has of things, by those ideas and appearances which God has fitted it to receive from them, and how the