The interaction problem

The “interaction problem”: how can the intellect be immaterial when no one can imagine how the immaterial can interact with the material?

It’s odd that people view this as an objection. I look at the same facts and view it as a proof. Of course you can’t imagine the interaction. That’s the whole point! Did you think we were kidding when we said “immaterial”? If I could imagine the interaction, then I’d be wrong! Don’t you see that I’m insisting that you can’t imagine any interaction?

What then? does anyone want to insist that what is, is imaginable? That’s a relic of “space and time” Kantianism that thought Newtonianism was the end of scientific history.


  1. Peter said,

    February 26, 2009 at 8:08 am

    —Disputed Questions on the Soul art. 1 corpus—
    On the contrary, a thing receives its species through its proper form. But man is man because he is rational. Hence the rational soul is the proper form of man. Moreover the soul is a particular self-subsisting thing because it operates of itself; for its act of understanding is not performed through a bodily organ, as is proved in the De anima [III, 4 (429a 24)]. Consequently the human soul is a particular thing and a form.

    Further, the highest perfection of the human soul consists in knowledge of truth which is acquired through the intellect. Moreover the soul must be united to the body in order to be ‘perfected in knowledge of truth, because it understands through phantasms which are non-existent without the body. Consequently the soul must be united as a form to the body and must be a particular thing as well.

    I answer: “A particular thing,” properly speaking, designates an individual in the genus of substance. For the Philosopher says, in the Categories [V, 2a 10], that first substances undoubtedly signify particular things; second substances, indeed, although they seem to signify particular things, rather signify the specific essence (quale quid). Furthermore, an individual in the genus of substance is capable not only of subsisting of itself, but is also a complete entity belonging to a definite species and genus of substance. Wherefore the Philosopher, in the Categories [V, 3a 28], also calls a hand and a foot, and things of this sort, parts of substances rather than first or second substances. For although they do not exist in another as a subject (which is characteristic of a substance), they still do not possess completely the nature of a species. Hence they belong to a species or to a genus only by reduction.

    Now some men have denied that the human soul possesses these two real characteristics belonging to a particular thing by its very nature, because they said that the soul is a harmony, as Empedocles did, or a combination [of the elements], as Galen did, or something of this kind. For then the soul will neither be able to subsist of itself, nor will it be a complete thing belonging to a species or genus of substance, but will be a form similar only to other material forms.

    But this position is untenable as regards the vegetal soul, whose operations necessarily require some principle surpassing the active and passive qualities [of the elements] which play only an instrumental role in nutrition and growth, as is proved in the De anima [II, 4. 415b 28]. Moreover, a combination and a harmony do not transcend the elemental qualities. This position is likewise untenable as regards the sentient soul, whose operations consist in receiving species separated from matter, as is shown in the De anima [II, 12, 424a 16]. For inasmuch as active and passive qualities are dispositions of matter, they do not transcend matter. Again, this position is even less tenable as regards the rational soul, whose operation consists in understanding, and in abstracting species not only from matter, but from all individuating conditions, this being required for the understanding of universals. However, in the case of the rational soul something of special importance must still be considered, because not only does it receive intelligible species without matter and material conditions, but it is also quite impossible for it, in performing its proper operation, to have anything in common with a bodily organ, as though something corporeal might be an organ of understanding, just as the eye is the organ of sight, as is proved in the De anima [III, 4, 429a 24]. Thus the intellective soul, inasmuch as it performs its proper operation without communicating in any way with the body, must act of itself. And because a thing acts so far as it is actual, the intellective soul must have a complete act of existing in itself, depending in no way on the body. For forms whose act of existing depends on matter or on a subject do not operate of themselves. Heat, for instance, does not act, but something hot.

    For this reason the later Greek philosophers came to the conclusion that the intellective part of the soul is a self-subsisting thing. For the Philosopher says, in the De anima [III, 5, 430a 24], that the intellect is a substance, and is not corrupted. The teaching of Plato [Phaedrus, 24] who maintains that the soul is incorruptible and subsists of itself in view of the fact that it moves itself, amounts to the same thing. For he took “motion” in a broad sense to signify every operation; hence he understands that the soul moves itself because it moves itself by itself.

    But elsewhere [Alcibiades, 25-26] Plato maintained that the human soul not only subsisted of itself, but also had the complete nature of a species. For he held that the complete nature of the [human] species is found in the soul, saying that a man is not a composite of soul and body, but a soul joined to a body in such a way that it is related to the body as a pilot is to a ship, or as one clothed to his clothing. However, this position is untenable, because it is obvious that the soul is the reality which gives life to the body. Moreover, vital activity (vivere) is the act of existing (esse) of living things. Consequently the soul is that, which gives the human body its act of existing. Now a form is of this nature. Therefore the human soul is the form of the body. But if the soul were, in the body as a pilot is in, a ship, it would give neither the body nor its parts their specific nature. The contrary of this is seen to be true, because, when the soul leaves the body, the body’s individual parts retain their original names only in an equivocal sense. For the eye of a dead man, like the eye of a portrait or that of a statue, is called an eye equivocally; and similarly for the other parts of the body. Furthermore, if the soul were in the body as a pilot in a ship, it would follow that the union of soul and body would be an accidental one. Then death, which brings about their separation, would not be a substantial corruption; which is clearly false. So it follows that the soul is a particular thing and that it can subsist of itself, not as a thing having a complete species of its own, but as completing the human species by being the form of the body. Hence it likewise follows that it is both a form and a particular thing.

    Indeed, this can be shown from the order of natural forms. For we find among the forms of lower bodies that the higher a form is, the more it resembles and approaches higher principles. This can be seen from the proper operation of forms. For the forms of the elements, being lowest [in the order of forms] and nearest to matter, possess no operation surpassing their active and passive qualities, such as rarefaction and condensation, and the like, which appear to be material dispositions. Over and above these forms are those of the mixed bodies and these forms have (in addition to the above mentioned operations) a certain activity, consequent upon their species, which they receive from the celestial bodies. The magnet, for instance, attracts iron not because of its heat or its cold or anything of this sort, but because it shares in the powers of the heavens. Again, surpassing these forms are the souls of plants, which resemble not only the forms of earthly bodies but also the movers of the celestial bodies inasmuch as they are principles of a certain motion, themselves being moved. Still higher are brute beasts’ forms, which now resemble a substance moving a celestial body not only because of the operation whereby they move bodies but also because they are capable of knowledge, although their knowledge is concerned merely with material things and belongs to the material order (for which reason they require bodily organs). Again, over and above these forms, and in the highest place, are human souls, which certainly resemble superior substances with respect to the kind of knowledge they possess, because they are capable of knowing immaterial things by their act of intellection. However, human souls differ from superior substances inasmuch as the human soul’s intellective power, by its very nature, must acquire its immaterial knowledge from the knowledge of material things attained through the senses.

    Consequently the human soul’s mode of existing can be known from its operation. For, inasmuch as the human soul has an operation transcending the material order, its act of existing transcends the body and does not depend on the body. Indeed, inasmuch as the soul is naturally capable of acquiring immaterial knowledge from material things, evidently its species can be complete only when it is united to a body. For a thing’s species is complete only if it has the things necessary for the proper operation of its species. Consequently, if the human soul, inasmuch as it is united as a form to the body, has an act of existing which transcends the body and does not depend on it, obviously the soul itself is established on the boundary line dividing corporeal from separate substances.

  2. Peter said,

    February 26, 2009 at 3:31 pm

    On reading your post again, I got to wondering: is that really their objection? (That they can’t imagine it?) I have little to no interest in PoM stuff, so I’m not up on what they say.

  3. February 26, 2009 at 11:12 pm

    I’m all but certain that those who see the the interaction problem as a problem would not use the word “imagine” as opposed to “thought” or “mind”, but that’s exactly what I think the problem is. In a word, I think the interaction problem presupposes that one hasn’t made a clear distinction between to imagine and to understand by way of the objects that either gets a hold of.

  4. John said,

    January 21, 2010 at 7:13 am

    Imaginability depends upon whether experience has components. If conscious experience contained objects arranged in space and time you could imagine that these could be identical to physical objects.

    My intellect involves objects being arranged in space and time. Even “inner speech” is like sounds arranged between and around my ears (ie:spatial and temporal). (I define space as more than one thing continuously present, this is an adequate description for modelling experience geometrically).

    So yes, I will insist that “what is, is imaginable” but I would not use Newtonian spacetime for my model of space and time, I would accept what appears and try to describe this arrangement using modern geometrical ideas.

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