HumeвЂ™s first principle in his theory of human cognition is that вЂњideas are weak sense impressions.вЂќ That means, to put it another way, that the order of intellection is not different from the order of sensation, except in extrinsic and accidental ways. How, then, does this bear on the acts of knowing whereby we know the physical world? If one trusts the grandfather of contemporary philosophies of science, Hume, it has no bearing whatsoever. Thomas explains how the sacraments can confer grace, even though they are of themselves mere material beings.

It is through the distinctions just made that St. Readers who would like to study this further might consult especially St. One can recognize that this must be true in all cases an instrument is, by definition, subordinate to causing an effect which it really has the power to bring about, but only in a transitory way. It thus evidently has this power only in a transitory way, precisely by virtue of its instrumental subordination to a principal cause which in this case is reason.

And yet it can be said that speech does have the power to communicate thought. In speech, we communicate acts of the mind, which are not in the inherent power of mere sounds to communicate. In an earlier post I gave the example of speech. Yet instrumental causes do things, as instruments, that are not in their own inherent power. Will it still be true, then, that there is nothing in the effect that is not in the cause - including the instrumental cause? It must be true, if the instrument is genuinely a cause. But we understand an instrumental cause to be one through which a principal cause acts. Insofar as an efficient cause is a cause and its effect an effect, there is nothing in the effect that is not first in the cause.

Efficient causes give being to their effects. We can come at this another way, to make it clearer. But this is also true in the order of efficient causality: the instrument may be said to be doing something which it nevertheless does not do of itself if it did then it would be a principal cause, and only apparently subordinate. In the order of final causality, it is thus the principal cause, and not the instrumental cause, that has the end primarily the instrument has it by virtue of its subordination. An instrument is, by definition, what acts in subordination to a principle cause, towards an end given to it by a principal cause. LetвЂ™s start with what instrumental causality is. Yet it is of no small importance if one would have a true understanding of the nature of the physical sciences. But this, again, is largely passed over in customary discussions of the philosophy of science. As the natural sciences have progressed in what I earlier called the order of concretion, the role of instrumental causality has necessarily become greater and greater, for reasons I will explain below. And although it is present in our acts of knowing even from the very start, its role in science has not remained static. It is scarcely possible to underestimate the importance of this, even though it has been given almost no attention up until now.Д«ut the principle of instrumental causality is relevant to the philosophy of science for a second, equally important reason: because it is involved in our own acts of knowing by which we learn about the physical world. My essay linked on the sidebar - вЂњAnimals, Inertia, and Projectile MotionвЂќ - shows just how important this is, in fact, because the whole вЂњculture of forceвЂќ which originated in classical physics is, to a large extent, due to a failure to apprehend the role of instrumental causality in physical local motion. Therefore that object cannot be understood without understanding the role that instrumental causality plays in it. There are two ways in which the principle is relevant to discussions of natural science: first, because it is a part of the order of natural causality itself, or in other words a part of the object of our science. In my last post, I said I would discuss this principle of instrumental causality, and show how it has very important consequences.

Principle of causality