Shall we then rest contented with these two relations of contiguity and succession, as affording a complete idea of causation? By, no means. An object may be contiguous and prior to another, without being considered as its cause. There is a NECESSARY CONNEXION to be taken into consideration; and that relation is of much greater importance, than any of the other two above-mention'd.Here again I turn the object on all sides, in order to discover the nature of this necessary connexion, and find the impression, or impressions, from which its idea may be deriv'd. When I cast my eye on the known Qualities of objects, I immediately discover that the relation of cause and effect depends not in the least on them. When I consider their relations, I can find none but those of contiguity and succession; which I have already regarded as imperfect and unsatisfactory.1 (...)John Locke said "there is nothing in the intellect which was not previously in the senses", to which Leibniz appended, "except the intellect itself". Mises would have agreed with Locke on that account. Where Leibniz said "the intellect", Mises would have said, "the logical structure of the human mind".
What is our idea of necessity, when we say that two objects are necessarily connected together. Upon this head I repeat what I have often had occasion to observe, that as we have no idea, that is not deriv'd from an impression, we must find some impression, that gives rise to this idea of necessity, if we assert we have really such an idea. In order to this I consider, in what objects necessity is commonly suppos'd to lie; and finding that it is always ascrib'd to causes and effects, I turn my eye to two objects suppos'd to be plac'd in that relation; and examine them in all the situations, of which they are susceptible. I immediately perceive, that they are contiguous in time and place, and that the object we -call cause precedes the other we call effect. In no one instance can I go any farther, nor is it possible for me to discover any third relation betwixt these objects. I therefore enlarge my view to comprehend several instances; where I find like objects always existing in like relations of contiguity and succession. At first sight this seems to serve but little to my purpose. The reflection on several instances only repeats the same objects; and therefore can never give rise to a new idea. But upon farther enquiry I find, that the repetition is not in every particular the same, but produces a new impression, and by that means the idea, which I at present examine. For after a frequent repetition, I find, that upon the appearance of one of the objects, the mind is determin'd by custom to consider its usual attendant, and to consider it in a stronger light upon account of its relation to the first object. 'Tis this impression, then, or determination, which affords me the idea of necessity.(...)
I begin with observing that the terms of efficacy, agency, power, force, energy, necessity, connexion, and productive quality, are all nearly synonymous; and therefore 'tis an absurdity to employ any of them in defining the rest. (...)
The idea of necessity arises from some impression. There is no impression convey'd by our senses, which can give rise to that idea. It must, therefore, be deriv'd from some internal impression, or impression of reflection. (...)
This therefore is the essence of necessity. Upon the whole, necessity is something, that exists in the mind, not in objects; nor -is it possible for us ever to form the most distant idea of it, considered as a quality in bodies. (...)
the necessity or power, which unites causes and effects, lies in the determination of the mind to pass from the one to the other.2
"The logical structure of the human mind" refers to the built-in rules of inference in our minds that are ultimately given, because they cannot be inferred from any principles outside of themselves...
- inferring final causes
- the categories of deductive logic
- inferring causation from regular contiguity/succession
- inferring future regularity from past regularity (induction)
What is not understood however is that Hume would also agree with Leibniz's dictum. As can be seen in the above passages, he recognized that there must be some "determination of the mind" to make the leap from regular contiguity/succession to causation. This irreducible "determination of the mind" is basically what Mises was talking about when he wrote of "the logical structure of the human mind."
1David Hume, A Treatise of Human Nature, Book 1, Part 3, Section 2
2Ibid, Book 1, Part 3, Section 14