Thursday, June 9, 2022

The mind-world similarity thesis

Eventually, the modern tradition becomes very suspicious the idea that there can be a similarity between the contents of the mind and characteristics of things in the external world. First, we have Locke denying the possibility of the similarity thesis for secondary qualities like red and sweet, and then we have others, like Berkeley and Reid, denying the possibility of the similarity thesis for primary qualities, like triangularity. In the case of primary qualities, it just seems absurd to think that the mind should hold something like a triangle.

This denial of the possibility of the similarity thesis seems to me to be a massive failure of the philosophical imagination, and a neglect of a sympathy to the history of philosophy. The allegation of the absurdity of thinking that triangularity should be present in the mind and in the world seems to come from thinking that the only way triangularity can be present in an entity is by the entity’s having triangularity. But why should having be the only possible relation by which triangularity could be present in a thing?

Here are some ways in which a property could be in a thing without the thing having the property.

  • Let S be the set of the polygonality properties. Thus, the members of S are triangularity, quadrilaterality, etc. Triangularity is then in S qua member of S, but S is not a triangle—it does not have triangularity.

  • On divine simplicity, God is identical with his divinity. But God can be present in Francis without Francis having God’s divinity—i.e., without Francis being divine.

  • Suppose that I have a wood triangle in a steel box. The triangle’s triangularity is in the triangle, and the triangle is in the box, so the triangularity is in the box.

  • Say that my fingernail is pointy. The properties of a thing are parts of a thing. So, the fingernail has its pointiness as a part. But the fingernail is a part of me, and parthood is transitive. So the pointiness of the fingernail is a part of me. But I am not pointy, even though I have a pointiness in me.

There is nothing absurd, then, about there being triangularity in the mind without the mind being itself triangular.

Moreover, having triangularity in the mind is not even a necessary condition for there to be a relevant similarity between the mind and a wooden triangle outside of me. It could be that the triangularity in the triangle is not a simple entity, but is composed of two components, T and P, where the P component is common (either as type or as token) between all properties, and the T component distinguishes triangularity from other properties. Thus, squareness might consist of S and P, and redness might consist of R and P. Well, then, we can suppose that when I think of or perceive a triangle as a triangle, then T comes to be in my mind without P doing so. Perhaps T comes to be “elementally” present in my mind, or perhaps it comes to be compounded with something else. (Here is a Thomistic version: triangularity has an essence T and a natural esse P; when present in the mind, the essence is there, but instead comes to have a different thing from the natural esse, say an intentional esse.) In either case, we have something importantly in common between the mind and the triangle qua triangular, namely T, without having triangularity in the mind, but only a component of triangularity.

There is no paucity of options. Indeed, we have an embarrassment of riches—many, many ways of making the similarity thesis true.


Kenny Pearce said...

I think the issue here has to do with the metaphysics of properties. If you think of substances and properties as existing independently and being related to one another by the relation of instantiation or predication then there's no reason why there shouldn't be a variety of relations in which a substance can stand to a property, and knowledge/cognition could be one such relation. (John Sergeant, a neo-Aristotelian direct realist critic of Locke, seems to make this kind of move in the late 17th century.) But it's much harder to see how this would work on a nominalist view, and it certainly won't work under Cartesian metaphysics. In Cartesian metaphysics, the principal attribute is not really distinct from the substance itself, and every (fundamental) property possessed by a substance must be a modification of its principle attribute—i.e., a manner of thinking or a manner of being extended. So we can't see the properties as separate from the substances in such a way as to allow a plurality of relations to different substances. The property (mode) is the substance's manner of being.

Now Arnauld (and maybe Descartes?) takes the modes of thought to possess intentionality intrinsically and primitively, and hence to relate the mind to objects, including external ones. But Malebranche thinks the modes of mind are just sensations—phenomenal feels, without intrinsic intentionality or representational content. Once you start thinking of thought in terms of phenomenal experience, rather than in terms of representation/intentionality, you don't have Arnauld's move available, and the question becomes just the one Berkeley poses: how could a sensation, a phenomenal feel, or anything like it be in an unthinking object?

Alexander R Pruss said...


Interesting point about nominalism. It hadn't occurred to me that all these folks might be nominalists. And I am still not sure they are. The language of "modification" does not imply nominalism. Modifications can still exist, even if their existence is dependent on that of which they are modifications. Spinoza, for instance, thinks we are modifications of modifications, but I don't think he would want to deny his own existence--just his substantiality. Leibniz seems quite happy to quantify over appetitions and perceptions, and we have no indication that these don't exist--just they don't substantially exist.

In other words, the language of modifications or manners fits quite fine with what contemporary folks call a trope theory, and all my examples were meant to work within a trope theory. Indeed, it is not clear that either my triangle or my fingernail cases work on Platonism, because it's not clear that on Platonism the properties are IN the substance that has them.

Do Berkeley and Locke deny that phenomenal qualities are entities, even if dependent ones? If they don't deny it, they aren't nominalists (or at least not consistent ones).

Kenny Pearce said...

By 'nominalism' I mean the denial of the mind- and language-independent existence of universals. 'Nominalism' in the strict sense maintains that only words or other signs can be universal or general. 'Nominalism' in the broad sense allows that mental states (concepts, ideas, etc.) may also be universal or general. Nearly all early moderns are standardly interpreted as nominalists in the broad sense. Hobbes is clearly a nominalist in the narrow sense, and I think Berkeley is as well.

This is consistent with the existence of tropes, or something similar. Tropes are individuals, not universals. Tropes can't be had in common by multiple objects.

The standard read on Descartes would be that individual modes (e.g., the roundness of this apple) exist but are not really distinct from their substances (e.g., the apple). Meanwhile, he's standardly interpreted to deny the existence of an (immanent or transcendent) universal roundness. E.g., there's no sense in which the same roundness exists in multiple apples. The picture is complicated a bit by the theory of true and immutable natures, though.

I thought your discussion was committed to universals (though immanent, Aristotelian ones would be fine) because the whole thing appears to turn on the notion that the same property can be 'in' different objects (in a variety of ways). On the Cartesian metaphysics of modification, a mode's very being consists in a substance possessing its principal attribute in a particular way. It's then hard to see how the mode could exist 'in' anything other than the substance it modifies. However, Descartes's notion of 'objective being' requires it to! Hence, his followers are left with a philosophical puzzle.

Alexander R Pruss said...


Well, any nominalist who isn't crazy and who accepts tropes has some way of explaining how two different things are triangular or two different minds are in pain. The standard way is to say that two different things can have exactly similar (or sufficiently similar) tropes, with the similarity being a fundamental piece of the ideology. I think everything I wrote can be made to fit with that.

Let me go through my four examples.

The first one, I must now admit, was written in Platonist style. But the example does not require Platonism about properties. Just let S the set of the polygonality properties of actually existing objects (stop signs, yield signs, watch faces, etc.) Then the individual triangularity of an individual yield sign is "in" S, even though S isn't a triangle.

The second could be read in a Platonist way, but I would prefer not to. God dwells in St Francis, as is evident from St Francis's holy life. But God is identical to God's trope of divinity according to divine simplicity. So God's trope of divinity is IN St Francis, even though St Francis isn't divine (at least in the sense in which God is; I don't mean to deny theosis).

The third is straightfoward. The individual triangularity of the wooden triangle is IN the wooden triangle, which in turn is in a steel box, which steel box is, we may suppose, a rectangular prism rather than a triangle. Being-in is transitive, so the particular triangularity of the wooden triangle is IN the steel box, without the steel box being triangular.

The fourth is very similar. The individual pointiness of my nail is in my nail, and my nail is in me, so the pointiness is IN me, without me being pointy. (Variant: The individual redness of my blood is in the blood, the blood is in me, but I am not red.)

On reflection, I could imagine one of the moderns criticizing these examples on the grounds that in all these cases, the individual trope or mode or accident that is in the thing that doesn't have the relevant property is ALSO, and more fundamentally, in a thing that does have the property. Thus, while I am not pointy, the pointiness is in my nail, which IS pointy. And the divinity that is in Francis is also in God, and more fundamentally so. But it seems that if an individual triangularity is in my mind, then it isn't the triangularity of any particular triangle.

Maybe, but maybe not. One could have a theory on which the particular trope that is in my mind is a trope of some particular thing that is modified by that trope. Perhaps the individual triangularity that is in my mind when I think of triangles is the very triangularity of the first individual triangle I ever encountered. (Since a number of the folks in question are empiricists, they should not object that we can have concepts of things unencountered.) One might wonder how that individual triangularity can continue to exist when it is dependent on a triangular substance that might well have been destroyed by now. Well, Descartes as a Catholic at least should be OK with that, since the doctrine of transubstantiation as usually interpreted requires the persistence of the accidents of bread and wine after the destruction of their substance. And, in any case, if one is an eternalist, like I am, one can embrace the idea of a triangularity depending on a pastly existent substance.

Alexander R Pruss said...

Or one could have a theory on which tropes normally exist in substances that they modify, but there can be unaffiliated tropes. Some current trope theories have these. To make them more plausible, suppose they are produced and preserved by the power of God. Aquinas has the nice principle that whatever can be accomplished by creatures can be accomplished by God without the help of the creatures. If I have the power to produce my tallness and then preserve it (by growing tall and staying tall), God has the power to produce a tallness and preserve it without any creature being involved. That tallness could then exist in a mind.

Granted, one may think that these ideas are crazy. But while I admit they are strange, they are less crazy than the anti-realism of a Berkeleian view.

And there are other options, such as the parts-of-tropes view I give at the end of the post.

The point is that there are MANY ways out of the arguments, and it is simply a massive shortfall in philosophical imagination to accept the arguments without arguing against the many ways out.

Kenny Pearce said...

I guess there's an ambiguity here about 'contents of the mind' here. Descartes is comfortable talking about objective being as being in the mind in the way objects are normally there, and gives no explanation of how this works. Obviously he's committed to the claim that things in the mind in THAT way (i.e., as intentional objects) can resemble things in the world, and some of his followers, such as Arnauld, are happy to follow him in that.

A non-physical, simple Cartesian mind can't physically (spatially) contain anything, and can't have anything as a part, so those two examples are out. Set membership obviously is also out. The divine indwelling case is interesting (and many of these philosophers are committed to its possibility) but it's not easy to make sense of. In any event, none of these four relations could be the relation of a Cartesian ego to the modes of extension. A sui generis relation is needed, which Arnauld (and perhaps also Descartes) accepts.

Descartes's metaphysics is totally inconsistent with transubstantiation and his attempts at reconciling the two are not promising, nor does he devote a huge amount of effort to this. (See: That a mode can't jump from one substance to another, or persist apart from its substance, is a principle Descartes appeals to in his physics and metaphysics. Additionally, he needs it to be an a priori necessary truth or else the 'thought without a thinker' objection to the cogito becomes extremely pressing.

In any event, I think the view endorsed by most early moderns would be better phrased as: no mode of a material object can have any resemblance to a mode of a mind. The question posed by Berkeley is then: how can minds represent objects that have no resemblance to the mind's representation? Prior to Berkeley, Arnauld had tried to get around this problem by taking intentionality/representational content as primitive and not involving resemblance between act and object, while Malebranche had tried to get around it by denying that ideas are modes of finite minds.

I'm not saying that there aren't ways out of the argument. I'm saying that the most early modern philosophers (unlike most medieval philosophers) were working within a metaphysical framework that appears to block the ways out.

Alexander R Pruss said...


Even if the particular examples are out, once we have seen that with a little bit of thought we have found so a bunch of ways of one a property being "in" something that doesn't have that property, we really shouldn't have much confidence that there isn't some other way we haven't yet given. This is, I guess, the sui generis move.

That said, here are two further options. First, while the soul is simple, it isn't completely simple in the way that God is on classical theism. It could well be that the soul is only lacking what one might call "integral parts" in Thomistic jargon, but still has some ontological complexity. If so, why couldn't it have a trope as a non-integral part without this property qualifying it?

Second, even if the soul has no parts of any sort, I don't think we have any good argument that tropes themselves are simple. And if they're not, there are lots of options.