In a sense the mind-body problem is in reality a whole set of problems which are all based on an alleged insurmountable difference between the mental and the physical.

But this question is about the mind-body problem with a focus on the problem of subjective conscious experience (not intentionality etc). There are very well known formulations of it. For example:

It must be confessed, moreover, that perception, and that which depends on it, are inexplicable by mechanical causes, that is, by figures and motions, And, supposing that there were a mechanism so constructed as to think, feel and have perception, we might enter it as into a mill. And this granted, we should only find on visiting it, pieces which push one against another, but never anything by which to explain a perception. This must be sought, therefore, in the simple substance, and not in the composite or in the machine.
(Gottfried Wilhelm Leibniz, Monadologie)


it is easy for us to suppose [...] that we ourselves have no hands or feet, or indeed any body at all. But we cannot for all that suppose that we, who are having such thoughts, are nothing. For it is a contradiction to suppose that what thinks does not, at the very time when it is thinking, exist. Accordingly, this piece of knowledge — I am thinking, therefore I exist — is the first and most certain of all to occur to anyone who philosophizes in an orderly way. This is the best way to discover the nature of mind and the distinction between the mind and the body.
(René Descartes, Principia philosophiae)

I think these are easily understandable and still powerful arguments (maybe after a small update) against physicalism (and the usual counterarguments are at least problematic, but I won't go into details).

Both examples above are from the early modern period.

Now has any western philosopher from antiquity or the middle ages made a similar argument?

The arguments seem so obvious, it seems unthinkable that no earlier philosopher had similar ideas.

But, if indeed the early moderns were the first, how could one explain this?


1 Answer 1



In his work On the Soul, Aristotle distinguishes Anaxagoras from the other philosophers for his belief that the soul is free from multiplicity as well as having nothing in common with anything else. Of course, this suggests that the soul must be distinct from the material world:

"Anaxagoras, as we said above, seems to distinguish between soul and mind, but in practice he treats them as a single substance, except that it is mind that he specially posits as the principle of all things; at any rate what he says is that mind alone of all that is simple, unmixed, and pure." (De Anima, 1, 405a13-16)

Aristotle goes on to explain that the mind cannot have anything in common with or be a mixture of anything else, because otherwise such impurity would inhibit the mind's ability to "dominate" objects through the act of thinking.

"Therefore, since everything is a possible object of thought, mind in order, as Anaxagoras says, to dominate, that is, to know, must be pure from all admixture; for the co-presence of what is alien to its nature is a hindrance and a block." (De Anima, 4, 429a18-20)


Aristotle's own view seems to be much in agreement with that of Anaxagoras. He describes the unmixed purity of the mind while emphasizing its essentially active nature. Along with this active factor, he also attributes to the mind a passive factor which he refers to as its "matter" (ὕλη). Just as a piece of warm wax can take on the shape of other objects, the mind has the capacity to take on the forms of objects in its activity of thinking and perception:

"Since in every class of things, as in nature as a whole, we find two factors involved, (1) a matter which is potentially all the particulars included in the class, (2) a cause which is productive in the sense that it makes them all (the latter standing to the former, as e.g. an art to its material), these distinct elements must likewise be found within the soul. And in fact mind as we have described it is what it is what it is by virtue of becoming all things, while there is another which is what it is by virtue of making all things: this is a sort of positive state like light; for in a sense light makes potential colours into actual colours. Mind in this sense of it is separable, impassible, unmixed, since it is in its essential nature activity (for always the active is superior to the passive factor, the originating force to the matter which it forms)." (De Anima, 5, 430a10-19)

Although Aristotle held that the soul must usually remain united with the body, he also spoke of the separation from it, in which case, the soul is impassible yet immortal:

"When separated it is alone just what it is, and this alone is immortal and eternal (we do not remember because, while this is impassible, passive mind is perishable); and without this nothing thinks." (De Anima, 5, 430a22-25)

Aristotle's inquiry into the nature of perception and dreams also suggests mental properties which are distinct from the material. In the following, he recognizes a common denominator between the imaginative faculty (φανταστικόν) and the perceptive faculty (αἰσθητικόν). This is something that many materialists try to deny because an identity between dreams and perceptions suggests that the phenomenal properties that are often assumed to belong to the material world are actually properties of the world within:

"But since we have discussed imagination in the treatise On the Soul, and the imaginative (φανταστικόν) is the same as the sensitive faculty (αἰσθητικόν), although the imaginative and the sensitive are different in essence; and since imagination is the process set up by a sense faculty in a state of activity, and a dream appears to be some sort of mental image (for an image which appears in sleep, whether simply or in a special sense, we call a dream); it is clear that dreaming belongs to the sensitive faculty but belongs to it qua imaginative." (De Insomniis 459a15-22)


Both Descartes and Malebranche were influenced by Augustine, so it should come as no big surprise that there are similarities in their views concerning the body and soul. Like Anaxagoras and Aristotle, Augustine presents another version of the sui generis argument, maintaining that the soul must be distinct in nature from that which is represented in consciousness. Augustine's argument appeals to the fact that sensation must be adequately suited to "spiritual vision" (visio spiritalis), as opposed to "bodily vision" (visio corporalis), in order for it to be intelligible:

"Bodily vision, which is the one which depends on the action of the external senses, is less noble than the spiritual vision which belongs to the imagination. But intellectual vision is more noble again than spiritual vision; bodily vision could not occur without spiritual vision, for at the same time as the body is affected in one of its senses, something similar occurs in the mind, i.e. in the origin of imagination or common sense, which is similar to what happens externally but is not the same thing. For if that were the case, this impulse which comes from outside us and by means of which we perceive external objects could not be called sensation, because it would not be accompanied by a thought of the soul. For the impulse is not connected with what happens externally except insofar as the latter is communicated to common sense. It is not the body which senses but the soul through the body, which she uses like a messenger to form in itself the idea of the thing which is presented to it externally. Bodily vision, therefore, cannot occur without spiritual vision, which consequently does not seem different from the first one until the senses cease to function and one finds in one's mind the images of things which were formerly perceived through the senses." (Genesis ad Litteram, 12.24.51)

In addition to that, Augustine also presents arguments for convincing people that images of objects are formed in the mind (De Trinitate, 11.2.3). One such argument draws the reader's attention to consider the nature of afterimages, and in the same section he also presents a double-vision argument. This latter argument is illustrated with the idea of a candle seen as double when the convergence of the eyes does not correctly fall upon the object observed:

"Why, even when the little flame of a lamp is in some way, as it were, doubled by the divergent rays of the eyes, a twofold vision comes to pass, although the thing which is seen is one. For the same rays, as they shoot forth each from its own eye, are affected severally, in that they are not allowed to meet evenly and conjointly, in regarding that corporeal thing, so that one combined view might be formed from both. [...] For it is enough for the business in hand to consider, that unless some image, precisely like the thing we perceive, were produced in our sense, the appearance of the flame would not be doubled according to the number of the eyes; since a certain way of perceiving has been employed, which could separate the union of rays. Certainly nothing that is really single can be seen as if it were double by one eye, draw it down, or press, or distort it as you please, if the other is shut." (De Trinitate, 11.2.4)


Thomas Aquinas was strongly influenced by Aristotle, and the influence of Augustine is evident in his work as well. Aquinas continues with Aristotle's idea of the mind taking on the forms of physical objects. In Aquinas' account, the idea of forms is used in three different senses:

  1. The form existing in the physical object and which may be received by the senses.

  2. The form which inheres in the mind. (See: IV Sententia d. 49, q. 2, a. 1.)

  3. The forms abstracted from their appearances and thus free from any material existence.

In the third sense, Aquinas sometimes used the Latin word species instead of the Latin forma:

"This is done by the power of the active intellect which by turning towards the phantasm produces in the passive intellect a certain likeness which represents, as to its specific conditions only, the thing reflected in the phantasm. It is thus that the intelligible species is said to be abstracted from the phantasm; not that the identical form which previously was in the phantasm is subsequently in the passive intellect, as a body transferred from one place to another." (Summa Theologica, Part I, Ques. 85)

What is particularly interesting about this is that it demonstrates continuity with the ideas of Anaxagoras, Aristotle and Augustine that the mind has a certain nature which is incompatible with the objects of perception. Therefore, according to the philosophy of Aquinas, there must be an adaptation from the physical to the phantasm and finally to the intelligible species. He supports this idea with the argument that intelligible species have to have the same mode of existence as the human intellect:

"But phantasms, since they are images of individuals, and exist in corporeal organs, have not the same mode of existence as the human intellect, and therefore have not the power of themselves to make an impression on the passive intellect." (Summa Theologica, Part I, Ques. 85)


The observations of these philosophers from antiquity highlight some of the properties which distinguish the mind and the soul from the physical world. In addition to that, each of them provided what might be considered a unified argument to the effect that conscious experience cannot be material because of a necessary incompatibility, but each of them approached it in a slightly different way. Anaxagoras' approach was that the intellect would be unable to "dominate" its objects of thought if there wasn't an ontological distinction to be made. Aristotle essentially agreed with Anaxagoras, but he also asserted that the active must be superior to the passive. Augustine argued that bodily vision alone would be inadequate because otherwise sensation would not be "accompanied by a thought of the soul." Finally, Aquinas asserted that an impression on the passive intellect could only be made provided that there is a common mode of existence with the human intellect.

As opposed to merely providing means for detecting properties which distinguish conscious experience from the material, these philosophers have approached the question by addressing the underlying necessity of those distinctions. Properly developed, such arguments are potentially much stronger than those aimed at simply identifying differences.

  • Very nice, well-researched answer. But most of it hasn't much to do with the question. Remember, the question was not if medieval or earlier philosophers thought about the mind-body-problem. Of course they did. The question was if they made arguments like the examples from Descartes or Leibniz. Arguments that subjective conscious experience cannot be material. So far, Augustine seems the only one. Anaxagoras, Aristotle and Aquinas focus more on intellectual activity.
    – viuser
    Mar 24, 2016 at 7:25
  • 1
    @vi user. I did understand that that was what you were asking, and my intention was to address precisely that question. However, it seems that I didn't make it clear enough, so I have edited the answer, adding a conclusion to a clarify how each of them provided an argument to that effect.
    – user3017
    Mar 24, 2016 at 9:45

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