According to medieval philosophers, the notion ofbeing is simple, indefinable, and in some sense precedes all other concepts we have. This, however, does not mean that it cannot be clarified. For instance, the notion of propositional conjunction is also simple and thus indefinable in terms of other, simpler concepts. Still, the notion can be clarified by describing the semantic function of the word expressing it in the following manner: the word ‘‘and’’ in English has the function of joining two propositional clauses in such a way that the conjunctive proposition expressed by the resulting compound sentence is true if and only if both propositions expressed by the clauses of the compound sentence are true. Likewise, we may provide a similar clarification of the notion of being through first characterizing the semantic functions of the words expressing it as these functions were typically conceived by medieval philosophers.
The English word ‘‘being’’ translates both the present tense active participle form ‘‘ens’’ and the infinitive form ‘‘esse’’ of the Latin verb ‘‘est,’’ corresponding to the English verb ‘‘is.’’ Just like the English verb, the Latin verb functions both as a copula, joining subject and predicate into a proposition, and as an absolute verb, asserting the existence of the thing referred to by the subject.
Influenced by the post-Kantian/Fregean mantra according to which ‘‘existence is not a predicate,’’ many contemporary philosophers might be inclined to part company with their medieval colleagues already at this point. However, this oft-quoted slogan in the sense in which it is trivially true is simply irrelevant, whereas in the sense in which it is clearly relevant, it is simply false. For, in the sense in which it expresses the claim that the verb ‘‘be’’ and its cognates (including ‘‘exists’’ and its derivatives) used in the sense in which they express a Fregean second order concept (a concept that operates on other concepts) do not express a first order concept (a concept true of things), the slogan is trivially true. But in that sense it is irrelevant, as it says nothing about how medieval philosophers could or could not use the verb ‘‘est’’ and its cognates (cf. Klima 2004). However, in the sense in which the slogan would claim that medieval philosophers could not have possibly used ‘‘est’’ and its cognates as a predicate, the slogan, though clearly relevant, is simply false, for our medieval colleagues just did use them as such. Indeed, they did so consistently, and reflectively, within the framework of some truly intriguing semantic considerations.
One question that immediately crops up if one reflects on the syntactic role of‘‘est’’ both as a copula (esse tertium adiacens) and as an absolute predicate (esse secundum adiacens) is whether it is a mere coincidence that it is the verb expressing existence that is used in both roles, both to copulate subject and predicate (to distinguish the resulting proposition from a mere list of names) and to predicate the actual existence of something. The question was already systematically considered by Abelard, who deployed an impressive array of arguments concerning the issue. However, his preferred theory, which would provide a noun-phrase/verb-phrase analysis of all categorical propositions (and thus would accord the copula the function of merely turning a nominal predicate term into a verb phrase), did not catch on, and did not have followers in the thirteenth century (cf. Jacobi 1986; King 2008).
The typical thirteenth century analysis followed Aristotle’s considerations, not only in the Peri Hermeneias known to Abelard, but also in Aristotle’s later recovered works, especially the two Analytics and the Metaphysics, along with Avicenna’s and Averroes’ immensely influential interpretations of Aristotle’s doctrine. These considerations suggested both that the copula is essential in all predications for joining two noun-phrases in a proposition (thus, even a verb is supposed to contain an implicit copula, and so is to be analyzed into a copula-plus-participle construction, such as ‘‘A man runs’’ = ‘‘A man is running’’) and that the sense of the verb ‘‘est’’ even in its copulative function is somehow related to or is even derivable from its existential sense. The idea is neatly expressed by Thomas Aquinas in his commentary on Aristotle’s Peri Hermeneias:
> The reason why [Aristotle] says that the verb 'is' cosignifies composition is that it does not principally signify composition, but secondarily; for it primarily signifies what occurs to the mind in the way of actuality absolutely: for 'is', uttered absolutely, signifies being in act, and hence it signifies as a verb. However, since actuality, which the verb 'is' principally signifies, is in general the actuality of every form (whether it is a substantial or an accidental actuality), when we want to signify any form or act to actually inhere [inesse] in a subject, we signify this by means of the verb 'is', either absolutely [simpliciter] or with some qualification [secundum quid]... (In Perihermeneias lb. 1, lc. 5, n. 22).
So, on Aquinas’ view, the verb ‘‘est’’ primarily signifies an act of being (esse or actus essendi) of that to which it is attributed (whether it is its substantial act, as in ‘‘Socrates is’’ or ‘‘Socrates is a man’’, or some accidental act, as in ‘‘Socrates is wise’’ or ‘‘Socrates is tall’’), and only secondarily signifies the composition of subject and predicate. Taking the verb ‘‘est’’ to signify an act of being (esse) is based on an analogy with any other verb that signifies some act, just as the verb ‘‘currit’’ (‘‘runs’’) signifies an act of running (currere) (cf. In De hebdomadibus lc. 2, n. 22). Thus, when ‘‘est’’ is used as an absolute predicate, when it is to be analyzed into copula and participle just as any other verb, as in ‘‘x est’’ = ‘‘x est ens’’, then ‘‘est’’ signifies the substantial act of being of x (as does the nominal predicate ‘‘ens’’), and it is the actuality of this act of being that verifies the predication. However, when ‘‘est’’ is construed with another predicate as the copula, as in ‘‘x est N’’, where ‘‘N’’ is some noun-phrase, then it still primarily signifies existence, although in a sense somehow modified by the content of the predicate, which signifies a form of the subject. In that case, the act of being signified by ‘‘est’’ is the act of being of the form signified by the predicate, which is the substantial act of being of the subject, provided the form signified by the predicate is the substantial form of the subject, or an accidental act of being of the subject, if the form signified by the predicate is an accidental form (cf. Klima 2002a).
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