ANAXAGORAS
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
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)
AUGUSTINE
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)
AQUINAS
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:
The form existing in the physical object and which may be received
by the senses.
The form which inheres in the mind. (See: IV Sententia d. 49, q.
2, a. 1.)
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)
CONCLUSION
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.
