|Section VII : Of The Idea Of Necessary Connexion Part I|
THE great advantage of the mathematical sciences above the moral consists in this, that the ideas of the former, being sensible, are always clear and determin- ate, the smallest distinction between them is immediately per- ceptible, and the same terms are still expressive of the same ideas, without ambiguity or variation.
An oval is never mis- taken for a circle, nor an hyperbola for an ellipsis.
The isos- celes and scalenum are distinguished by boundaries more ex- act than vice and virtue, right and wrong.
If any term be defined in geometry, the mind readily, of itself, substitutes, on all occasions, the definition for the term defined: or even when no definition is employed, the object itself may be presented to the senses, and by that means be steadily and clearly apprehended.
But the finer sentiments of the mind, the operations of the understanding, the various agitations of the passions, though really in themselves distinct, easily escape us, when surveyed by reflection; nor is it in our power to recall the original object, as often as we have oc- casion to contemplate it.
Ambiguity, by this means, is gradually introduced into our reasonings: similar objects are readily taken to be the same: and the conclusion becomes at last very wide of the premises.
One may safely, however, affirm, that, if we consider these sciences in a proper light, their advantages and disadvan- tages nearly compensate each other, and reduce both of them to a state of equality.
If the mind, with greater facility, re- tains the ideas of geometry clear and determinate, it must carry on a much longer and more intricate chain of reason- ing, and compare ideas much wider of each other, in order to reach the abstruser truths of that science.
And if moral ideas are apt, without extreme care, to fall into obscurity and confusion, the inferences are always much shorter in these disquisitions, and the intermediate steps, which lead to the conclusion, much fewer than in the sciences which treat of quantity and number. In reality, there is scarcely a proposi- tion in Euclid so simple, as not to consist of more parts, than are to be found in any moral reasoning which runs not into chimera and conceit.
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 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? By what invention can we throw light upon these ideas, and render them altogether precise and determinate to our intel- lectual view? Produce the impressions or original senti- ments, from which the ideas are copied.
These impressions are all strong and sensible. They admit not of ambiguity.
They are not only placed in a full light themselves, but may throw light on their correspondent ideas, which lie in ob- scurity. And by this means, we may, perhaps, attain a new microscope or species of optics, by which, in the moral sciences, the most minute, and most simple ideas may be so enlarged as to fall readily under our apprehension, and be equally known with the grossest and most sensible ideas, that can be the object of our enquiry.
To be fully acquainted, therefore, with the idea of power or necessary connexion, let us examine its impression; and in order to find the impression with greater certainty, let us search for it in all the sources, from which it may possibly be derived.
When we look about us towards external objects, and consider the operation of causes, we are never able, in a single instance, to discover any power or necessary con- nexion; any quality, which binds the effect to the cause, and renders the one an infallible consequence of the other. We only find, that the one does actually, in fact, follow the other.
The impulse of one billiard-ball is attended with motion in the second. This is the whole that appears to the outward senses.
The mind feels no sentiment or inward impression from this succession of objects: consequently, there is not, in any single, particular instance of cause and effect, any thing which can suggest the idea of power or necessary connexion. From the first appearance of an object, we never can conjecture what effect will result from it.
But were the power or energy of any cause discoverable by the mind, we could foresee the effect, even without experience; and might, at first, pronounce with certainty concerning it, by mere dint of thought and reasoning.
In reality, there is no part of matter, that does ever, by its sensible qualities, discover any power or energy, or give us ground to imagine, that it could produce any thing, or be followed by any other object, which we could denominate its effect.
Solidity, extension, motion; these qualities are all complete in themselves, and never point out any other event which may result from them. The scenes of the uni- verse are continually shifting, and one object follows another in an uninterrupted succession; but the power of force, which actuates the whole machine, is entirely concealed from us, and never discovers itself in any of the sensible qualities of body.
We know that, in fact, heat is a constant attendant of flame; but what is the connexion between them, we have no room so much as to conjecture or imagine. It is impossible, therefore, that the idea of power can be derived from the contemplation of bodies, in single instances of their operation; because no bodies ever discover any power, which can be the original of this idea. 
Since, therefore, external objects as they appear to the senses, give us no idea of power or necessary connexion, by their operation in particular instances, let us see, whether this idea be derived from reflection on the operations of our own minds, and be copied from any internal impression. It may be said, that we are every moment conscious of internal power; while we feel, that, by the simple command of our will, we can move the organs of our body, or direct the faculties of our mind.
An act of volition produces motion in our limbs, or raises a new idea in our imagination. This influence of the will we know by consciousness.
Hence we acquire the idea of power or energy; and are certain, that we ourselves and all other intelligent beings are pos- sessed of power. This idea, then, is an idea of reflection, since it arises from reflecting on the operations of our own mind, and on the command which is exercised by will, both over the organs of the body and faculties of the soul.
We shall proceed to examine this pretension; and first with regard to the influence of volition over the organs of the body. This influence, we may observe, is a fact, which, like all other natural events, can be known only by experi- ence, and can never be foreseen from any apparent energy or power in the cause, which connects it with the effect, and renders the one an infallible consequence of the other. The motion of our body follows upon the command of our will.
Of this we are every moment conscious.
But the means, by which this is effected; the energy, by which the will performs so extraordinary an operation; of this we are so far from being immediately conscious, that it must for ever escape our most diligent enquiry. For first: Is there any principle in all nature more mysterious than the union of soul with body; by which a supposed spiritual substance acquires such an influence over a material one, that the most refined thought is able to actuate the grossest matter? Were we empowered, by a secret wish, to remove mountains, or control the planets in their orbit; this extensive authority would not be more extraordinary, nor more beyond our comprehension.
But if by consciousness we perceived any power or energy in the will, we must know this power; we must know its connexion with the effect; we must know the secret union of soul and body, and the nature of both these substances; by which the one is able to operate, in so many instances, upon the other.
Secondly, We are not able to move all the organs of the body with a like authority; though we cannot assign any reason besides experience, for so remarkable a difference between one and the other.
Why has the will an influence over the tongue and fingers, not over the heart or liver? This question would never embarrass us, were we conscious of a power in the former case, not in the latter. We should then perceive, independent of experience, why the authority of will over the organs of the body is circumscribed within such particular limits.
Being in that case fully acquainted with the power or force, by which it operates, we should also know, why its influence reaches precisely to such boundaries, and no farther. A man, suddenly struck with palsy in the leg or arm, or who had newly lost those members, frequently endeavours, at first to move them, and employ them, in their usual offices.
Here he is as much conscious of power to command such limbs, as a man in perfect health is conscious of power to actuate any member which remains in its natural state and condition.
But consciousness never deceives.
Consequently, neither in the one case nor in the other, are we ever conscious of any power. We learn the influence of our will from experience alone.
And experience only teaches us, how one event constantly follows another; without in- structing us in the secret connexion, which binds them together, and renders them inseparable.
Thirdly, We learn from anatomy, that the immediate object of power in voluntary motion, is not the member itself which is moved, but certain muscles, and nerves, and animal spirits, and, perhaps, something still more minute and more unknown, through which the motion is successively propagated, ere it reach the member itself whose motion is the immediate object of volition.
Can there be a more certain proof, that the power, by which this whole operation is performed, so far from being directly and fully known by an inward sentiment or consciousness is, to the last degree, mysterious and unintelligible? Here the mind wills a certain event.
Immediately another event, unknown to ourselves, and totally different from the one intended, is produced: This event produces another, equally unknown: till at last, through a long succession, the desired event is produced. But if the original power were felt, it must be known: were it known, its effect also must be known; since all power is relative to its effect. And vice versa, if the effect be not known, the power cannot be known nor felt.
How indeed can we be conscious of a power to move our limbs, when we have no such power; but only that to move certain animal spirits, which, though they produce at last the motion of our limbs, yet operate in such a manner as is wholly beyond our comprehension? We may, therefore, conclude from the whole, I hope, without any temerity, though with assurance; that our idea of power is not copied from any sentiment or consciousness of power within ourselves, when we give rise to animal motion, or apply our limbs to their proper use and office.
That their motion follows the command of the will is a matter of common experience, like other natural events: But the power or energy by which this is effected, like that in other natural events, is unknown and inconceivable.
 Shall we then assert, that we are conscious of a power or energy in our own minds, when, by an act or command of our will, we raise up a new idea, fix the mind to the con- templation of it, turn it on all sides, and at last dismiss it for some other idea, when we think that we have surveyed it with sufficient accuracy? I believe the same arguments will prove, that even this command of the will gives us no real idea of force or energy.
First, It must be allowed, that, when we know a power, we know that very circumstance in the cause, by which it is enabled to produce the effect: for these are supposed to be synonymous.
We must, therefore, know both the cause and effect, and the relation between them.
But do we pretend to be acquainted with the nature of the human soul and the nature of an idea, or the aptitude of the one to produce the other? This is a real creation; a production of something out of nothing: which implies a power so great, that it may seem, at first sight, beyond the reach of any being, less than infinite.
At least it must be owned, that such a power is not felt, nor known, nor even conceivable by the mind. We only feel the event, namely, the existence of an idea, consequent to a command of the will: but the manner, in which this operation is performed, the power by which it is produced, is entirely beyond our comprehension.
Secondly, The command of the mind over itself is limited, as well as its command over the body; and these limits are not known by reason, or any acquaintance with the nature of cause and effect, but only by experience and observation, as in all other natural events and in the operation of external objects.
Our authority over our sentiments and passions is much weaker than that over our ideas; and even the latter authority is circumscribed within very narrow boundaries.
Will any one pretend to assign the ultimate reason of these boundaries, or show why the power is deficient in one case, not in another. Thirdly, This self-command is very different at different times. A man in health possesses more of it than one languishing with sickness.