The medieval theories of logic generally hold, at least as represented in the brilliant work of Thomas Aquinas, that non-existent being can be said of existent being because non-existent being can be said to exist in some ontologically distinct manner from actually existent being; that is, it can be said to exist as a sort of image or concept in the mind. Thus, we can actually speak about non-existing things because they have some sort of existence in the mind.

But this seems, perhaps, to still not account for a gap in our reference. For the medieval logician would still likely offer that a proposition is true iff the form represented by the predicate actually inheres in the subject (aka, the inherence theory of predication). But how can our concept of such a non-existing thing properly be in relation to any existing thing? How can it be true that some non-existing thing inheres in an existing thing?

We might form a concept of the non-existing thing in which the actually non-existing thing takes some mitigated sense of existence but this does not change the fact that such a concept represents what is actually a non-existent, one that can be said to have a relation to an existent. This would needless to say require an interesting dissection of medieval relational ontology.

Have medieval philosophers offered clarity or insight into the way in which non-existents can inhere in reality? If they don't actually inhere in reality, then what accounts for the reference within our propositions that possess meaning despite being mere negations?

Disclaimer: It is very likely that I appear a fool in this question, for I am nearly illiterate in medieval logic. So if my question makes it seem that I am speaking poorly for medieval philosophers, such is very likely. It is not my intention to speak for any medieval philosophers at all though. Corrections and insight are welcome, especially as regards the initial presumptions I make even in the methodology by which I am asking.

  • You can see Gyula Klima, The Changing Role of Entia Rationis in Mediaeval Semantics and Ontology (1993). Mar 14, 2016 at 15:39
  • @Bombardi: Please indicate a precise reference concerning Thomas' statement that "non-existent being can be said to exist in some ontologically distinct manner from actually existent being"; thanks.
    – Jo Wehler
    Mar 14, 2016 at 16:05
  • @JoWehler Aquinas never stated those exact words, but such is his view as regards entia rationis. This is evident in a number of his writings. One example is his account of privation in the Sentences. He distinguishes two ways of being: "For in one way being is said as it is divided by the ten genera... In another way being signifies the truth of a proposition... But not everything which is a being in the second way is a being also in the first way: for of a privation we can form an affirmative proposition, saying blindness is; but blindness is not something in the nature of things."
    – Bombadil
    Mar 14, 2016 at 16:19
  • @Bombardi Where is the quote from your last comment from? I know this distinction but I would like to know the context too.
    – Jo Wehler
    Mar 14, 2016 at 16:25
  • @JoWehler It is from Aquinas's work titled 'Sentences'. There are many other places where such a distinction might be found however. Here are a few more: De Ente 1, ST1-2 36.1, De Malo 1.1 ad. 19.
    – Bombadil
    Mar 14, 2016 at 16:56

1 Answer 1


Ens rationis = a being of reason is a “thing dependent for its existence upon reason or thought.“ The term being of reason contrasts to the term real being (ens in re extra animam). But of course being of reason does not exclude real being:

Two kinds of entia rationis are distinguished: those with a foundation in reality and those without one. The objects of logic, which include genera and species, e.g., animal and human, respectively, are entia rationis that have a foundation in reality, but are abstracted from it.

In contrast, mythical and fictional objects, such as a chimera or Pegasus, have no foundation in reality.

Blindness and deafness are also sometimes called entia rationis.

All quotes from Audi, Robert (Ed.): The Cambridge Dictionary of Philosophy. 1995

I consider this a clear introduction into the relation between both concepts.

I do not know whether medieval philosophers specified the kind of relation between a concept (ens rationis) and a real thing (ens in re extra animam) in a sense similar to the correspondence theory of truth. In later times discussing this relation leads into epistemology with new proposals, e.g., constructivist epistemologies.

  • I don't understand this. China and Pegasus have arms and legs like people and animals, why are they not considered abstractions of real things/reality? May 30, 2016 at 19:52
  • @Jack Maddington What do you mean by "China [...] have arms and legs [...]"? China is a country, not an animal.
    – Jo Wehler
    May 30, 2016 at 20:32
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    Sorry, that was an accident of my Swype keyboard. I meant to input chimera. May 30, 2016 at 21:37
  • @Jack Maddington The terms leg and arm are abstractions from real things, but chimera and Pegasus do not refer to real things. The parts do, the whole does not.
    – Jo Wehler
    Aug 14, 2016 at 9:03

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