Where we trace the principles of the human mind through a few steps...

Where we trace the principles of the human mind through a few steps, we may be very well satis- fied with our progress; considering how soon nature throws a bar to all our enquiries concerning causes, and reduces us to an acknowledgment of our ignorance. The chief ob- stacle, therefore, to our improvement in the moral or meta- physical sciences is the obscurity of the ideas, and ambiguity of the terms.

The principal difficulty in the mathematics is the length of inferences and compass of thought, requisite to the forming of any conclusion. And, perhaps, our prog- ress in natural philosophy is chiefly retarded by the want of proper experiments and phaenomena, which are often dis- covered by chance, and cannot always be found, when requisite, even by the most diligent and prudent enquiry.

As moral philosophy seems hitherto to have received less im- provement than either geometry or physics, we may con- clude, that, if there be any difference in this respect among these sciences, the difficulties, which obstruct the progress of the former, require superior care and capacity to be sur- mounted.

There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion, of which it is every moment necessary for us to treat in all our disquisitions. We shall, therefore, endeavour, in this section, to fix, if possible, the precise meaning of these terms, and thereby remove some part of that obscurity, which is so much complained of in this species of philosophy.

It seems a proposition, which will not admit of much dis- pute, that all our ideas are nothing but copies of our im- pressions, or, in other words, that it is impossible for us to think of anything, which we have not antecedently felt, either by our external or internal senses.

I have endeavoured[^1] to explain and prove this proposition, and have expressed my hopes, that, by a proper application of it, men may reach a greater clearness and precision in philosophical reasonings, than what they have hitherto been able to attain. Complex ideas, may, perhaps, be well known by definition, which is nothing but an enumeration of those parts or simple ideas, that compose them.

But when we have pushed up defini- tions to the most simple ideas, and find still more ambiguity and obscurity; what resource are we then possessed of?