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Tuesday, October 30, 2012



I can’t speak for all Thomists, but from my (high school) notes on An Introduction to Logic by Jacques Maritain:

A.1. Mammal is animal. (T)
A.2. Man is mammal. (T)
A.3. Therefore, man is animal. (sound)

B.1. Mammal is animal. (T)
B.2. A man is a mammal. (T)
B.3. Therefore, a man is an animal. (unsound)

The idea is that B is formally invalid because it’s a logical quadraped (four-term deductive syllogism): there’s a supposition of terms with the predicate in B.2. to the subject in B.1., i.e., the subject-term ‘mammal’ is in the logical or mental mode of existence, whereas the complete predicate ‘a mammal’ is in a real mode of existence (without the implication that any such singulars exist). Likewise, the judgments ‘man is a mammal’ and ‘a man is mammal’ are false.

Anyway, I’m not clear on the whys, wherefores and intricacies, but when traversing from the mental mode to the real mode, a bridge proposition is required to conjoin propositions having different modes of existence:

C.1. If ‘man is animal’ then ‘a man is an animal’.
C.2. Man is animal.
C.3. Therefore, a man is an animal.

So my thinking is that Thomists are aware of the issue you brought to light, it’s just that they deal with it differently. I think they may be able to do so because with their logical schema there’s no existential import without a material premise. Meaning, until one affirms ‘that is a man’ or ‘there is a man’ or ‘Socrates is a man’, real existence is not affirmed. (Iirc, that’s why Aristotle made a clear distinction between formal/minor logic and material/major logic—the former doesn’t import existence whereas the latter does. Modern logic seems to intertwine the formal with the material, for better or worse.)

I note a passing resemblance to this post in April.

The scholastics of the late thirteenth century were intrigued by the idea that the structure of language reflects the structure of thought, and that the structure of thought reflects the structure of reality. Thus the linguistic structure of the expression 'rational animal' reflects both our understanding of that expression, and the reality corresponding to it, i.e. the structure or 'ratio' of human nature itself. Going further, the differences between the linguistic expressions 'some man', 'every man', 'this man' etc must also reflect a difference in meaning or understanding, and therefore (also) a difference in reality. Thus (on this way of thinking) 'some rational animal' corresponds to a reality which has three components: the animality, the rationality, and finally the 'someness'. Hence 'someness' or particularity is just as much a 'mark' of 'some rational animal' as 'rational' and 'animal'.

I'm not saying this view is correct, just explaining why the medievals would have thought this. On the modern Fregean analysis, we have to reject the idea of a close correspondence between language, thought and reality. Doesn't Frege say that the sentences 'the king's carriage is drawn by four horses' and 'the king's carriage is drawn by white horses' have entirely different underlying structures? In the latter, 'white' is the property ascribed to the horses. In the former, we are assigning the number four to the concept 'horse that draws the King's carriage'.


It's a re-posting and a re-thinking but with improvements. You didn't comment on the earlier version. So I tought I'd 'bait' you again.

I don't disagree with what you say above, but you are not engaging the Fregean critique of the Thomist argument, which, as you know, comes from Avicenna, Ibn Sina, back in the days when the Muslims were producing some good philosophy.

Do you accept that there is a distinction between the mark of a concept and a property of a concept? And do you see that if there is that distinction, then the Avicennian-Thomist argument is thoroughly confused?

Furthermore, and apart from Frege, do you agree that I fairly reconstructed the argument? And can you honestly say that you follow it?


I think I do accept the distinction, and I agree that if there is such a distinction then the argument rests on a faulty premiss. But I don't think the argument is confused – merely, it may have a faulty premiss. I don't think it is an obvious confusion to suppose that 'one' stands to 'one man' just as 'rational' stands to 'rational animal'.

For example, when we talk about two men, are we really saying something about concepts? Are we really saying that the concept man is instantiated twice? Or when I say that a man exists, am I really talking about a concept?


The argument is confused because the subarguments -- the one in support of (2) and the one in support of (3) -- are based on the confusion of mark and concept.

But I want to concede something to you. When I say that a man exists or that men exist it certainly seems that I am talking about a man or men and not about a concept! But which man and which men?

As you know I reject Frege's instantiation theory of existence.

It could be that both approaches lead to incoherence.

I think you have already appreciated that the Thomist argument proves that a nature considered absolutely neither exists nor does not exist. Now you won't accept that! Right? It amounts to Meinong's doctrine of Aussersein.

Mark and property, not mark and concept. Merkmal und Eigenschaft, nicht Merkmal und Begriff.

>>As you know I reject Frege's instantiation theory of existence.

I was rather puzzled that your assault on the Aquinas/Avicenna theory above depends on assumptions that you apparently reject elsewhere. (I may be mistaken).

Unless I am missing the implications of my critique of Frege's theory of existence, that critique should be consistent with my rejection of the above argument.

It seems clear that if concept C is included in concept D, that is not the same as C's being predicable of D. E.g., *male* is included within *bachelor,* but the former is not predicable of the latter: no concept is male. *Rational* is included within *man,* but the former is not predicable of the latter: no concdept is rational.

Does the same hold for Thomistic natures? They are not Fregean concepts, but are constituents of the things that have them. Thus humanity is a constituent of Socrates. Nevertheless, this nature is not rational. It is Socrates that is rational, and surely there is a distinction between Socrates and his nature.

Frege brings up his mark-property distinction right before making his famous claim about existence. He says that existence is not a mark of any concept. I agree with that. What I reject is the notion that existence is a property of concepts.

My position is consistent as far as I can see.

greetings good Sir,

even granting the distinction between marks and properties, Avicenna's argument, it seems, still stands.

this is because, Avicenna says, there’s a distinction between the essence of something and its existence. now existence is either in one of two modes i.e., mental or extra-mental. a given essence then, in itself, is completely indifferent to either mode of existence. but if that is so, then it follows that it is also in itself indifferent to whatever property (e.g., universality, particularity, oneness, manyness, etc) that accompanies either mode of existence. however, mental and extra-mental existence are themselves disjunctively necessary for it; the different modes of existence (and the properties which accompany them) are non-essential only in the sense that they fall outside the essence considered absolutely. as such, it only is what it is (e.g., in the case of ‘man’, has ‘rational’ and ‘animal’ as ‘marks’).

what the 12th century Avicennian philosopher Tusi says may be helpful here:

“Quiddity can never be independent of ‘existence’ except in the intellect. This, however, should not be taken as meaning that ‘quiddity’ in the intellect is separated from ‘existence’, because ‘being in the intellect’ is itself also a kind of existence, namely, ‘mental existence’, just as ‘being in the external world’ is ‘external existence’. The above statement [i.e., that quiddity is separated from existence in the intellect] must be understood in the sense that the intellect is of such a nature that it can observe ‘quiddity’ alone without considering its ‘existence’. Not considering something is not the same as considering it to be non-existent.”


A fine restatement of the Avicennian position. But to restate a position is not to respnd to a criticism of it.

Dear Dr. Vallicella,

First, I think the translation you're working from is a bit clunky. Second, I think your reconstruction is inaccurate:

"1. A nature can be considered absolutely or according to the being it has in this or that individual." - Sort of. There are three states of the universal. The absolute nature corresponds to the universal *ante rem*, which can be considered as such or according to the being it has (or could have) in an individual (or individuals) (*in re*) or according to its being in the soul (*post rem*). The absolute nature, note, is thus not identical to the concept 'in the human soul,' which might sound strange, but Aquinas' idea (as I understand it) is that the human intellect recognizes that its own abstracted concept must be grounded both in the object from which it is abstracted and in the creator of that object which (who) is distinct from and grounds the being of both intellect and object. (Of course all three states of the universal must in fact be in the soul insofar as the soul knows them, but they are in the soul as three distinct modes of consideration.)

"2. If a nature is considered absolutely, then it is not one. For if oneness were included in the nature of humanity, e.g., then humanity could not exist in many human beings." No. I think what Aquinas means is that if nature is considered absolutely (*ante rem*), then it is not thereby considered as instantiated as a particular (*in re*).

"3. If a nature is considered absolutely, then it is not many. For if manyness were included in the nature of humanity, e.g., then humanity could not exist in one man, say, Socrates." - ...And again, considered absolutely (*ante rem*), it is also not thereby considered as instantiated in a human mind (*post rem*).

4. If a nature is considered absolutely, then it is neither one nor many, neither singular nor plural." - I.e., it is neither a unity in the intellect, nor a plurality in things.

"But surely it does not follow that the nature humanity is neither one nor many." - So correct, but Aquinas does not say this. 'Humanity' refers to the abstract concept in the intellect and this concept is one concept (although it is also instantiated or instantiable in many intellects).

"What Aquinas is doing above is confusing what Frege calls a mark (Merkmal) of a concept with a property (Eigenschaft) of a concept." No. What you and Frege want to call 'marks' of a concept, Thomas calls 'parts of the essence' (*partes essentiae*). He does not confuse these with the 'properties' (or accidents) of the nature (i.e., being instantiated either in real particulars or in souls).

I hope this is a good Thomist response. If you think it is not, please let me know.

"If being instantiated were a mark of man, then the concept man could not fail to be instantiated." - Right, in Thomistic terms, *esse* is not included in the essence of man.

"To put it another way, Aquinas confuses the 'is' of predication ('Socrates is a man') with the 'is' of subordination ('Man is an animal'). Man is predicable of Socrates, but animal is not predicable of man, pace Aristotle, Categories 3b5: no concept or nature is an animal. Socrates falls under man; Animal falls within man. Falling-under and falling-within are different relations." - I don't see how either Aristotle or Aquinas is confused about this. They mark this distinction by the distinction between primary and secondary substances, do they not? They seem to be well aware of the difference between defining a species (secondary substance) (e.g., 'man is a rational animal') and identifying an individual (primary substance) as a member of a species (e.g., 'Socrates is a man').

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