The first eight paragraphs of Hume’s Section 7 of his Enquiry tackles ideas and necessary connection. In summary, Hume comes to terms with ideas needing to be traced back to their original impressions in order to be fully understood; however, when it comes to necessary connections, there is no initial impression to originate the idea. Instead of having an impressional origin of necessary connection, we merely infer the connection through constant conjunction of the objects. Hume reasons that we, as humans, cannot rationalize the causal connections.

He gets to this conclusion by first turning from geometry and probability from the section prior. We turn from the things we know without ambiguity, to those rife with ambiguity, mental sentiments. This ambiguity serves as the chief obstacle in improving metaphysical sciences, in addition to the obscurity of ideas. Hume also makes an interesting point regarding metaphysical science: “Perhaps, our progress in natural philosophy is chiefly [held back] by the want of proper experiments and phenomena which are often discovered by chance, and cannot always be found, when requisite, even by the most diligent and prudent enquiry.” (372)

Hume moves on to state that the most obscure metaphysical ideas are power, force, energy, and necessary connection; therefore, he goes forth to attempt to remedy the ambiguity of the terms.

It’s paragraph four when Hume states that ideas are copies of impressions, or as stated more eloquently, we cannot think of something that we haven’t first felt, either externally or internally. Therefore, when we cannot make sense of simple ideas due to ambiguity, we should turn to the impressions made first as they are strong, sensible, and not ambiguous. The impressions will shed light on what was obscure, and by this, we may end up with a new way of looking at things, by which the smallest ideas may be enlarged so much they can be the object of our inquiries.  So, with this, let’s become acquainted with the impressions of necessary connections.

We can’t.

When we attempt to trace back the idea, we find that we cannot do so. Necessary connection is never found, and instead, we only find that one does in fact follow the other. The impulse of one billiard-ball is attended with motion on the second one, but we cannot feel impressions from this succession. Consequently, there is no particular instance of cause and effect to suggest the idea of necessary connection. By simply seeing an object, we cannot know the effect that will result from it, but if there were power of a cause discoverable by the mind, then we can foresee the effect, even without experience.

In the end, we come to the conclusion that there is no matter that will cause an impressional origin to necessary connection. “The universe is continually shifting, and one follows another in uninterrupted succession; but the power of force, which actuates the whole machine, is entirely concealed from us.” (373) As a final example, we know that heat is a constant attendant of flames, but we cannot imagine the connection necessary between them. “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.” (373)