Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the definition of person given by Boethius (De Duab. Nat.) is insufficient---that is, "a person is an individual substance of a rational nature." For nothing singular can be subject to definition. But "person" signifies something singular. Therefore person is improperly defined.

Objection 2: Further, substance as placed above in the definition of person, is either first substance, or second substance. If it is the former, the word "individual" is superfluous, because first substance is individual substance; if it stands for second substance, the word "individual" is false, for there is contradiction of terms; since second substances are the "genera" or "species." Therefore this definition is incorrect.

Objection 3: Further, an intentional term must not be included in the definition of a thing. For to define a man as "a species of animal" would not be a correct definition; since man is the name of a thing, and "species" is a name of an intention. Therefore, since person is the name of a thing (for it signifies a substance of a rational nature), the word "individual" which is an intentional name comes improperly into the definition.

Objection 4: Further, "Nature is the principle of motion and rest, in those things in which it is essentially, and not accidentally," as Aristotle says (Phys. ii). But person exists in things immovable, as in God, and in the angels. Therefore the word "nature" ought not to enter into the definition of person, but the word should rather be "essence."

Objection 5: Further, the separated soul is an individual substance of the rational nature; but it is not a person. Therefore person is not properly defined as above.

I answer that, Although the universal and particular exist in every genus, nevertheless, in a certain special way, the individual belongs to the genus of substance. For substance is individualized by itself; whereas the accidents are individualized by the subject, which is the substance; since this particular whiteness is called "this," because it exists in this particular subject. And so it is reasonable that the individuals of the genus substance should have a special name of their own; for they are called "hypostases," or first substances.

Further still, in a more special and perfect way, the particular and the individual are found in the rational substances which have dominion over their own actions; and which are not only made to act, like others; but which can act of themselves; for actions belong to singulars. Therefore also the individuals of the rational nature have a special name even among other substances; and this name is "person."

Thus the term "individual substance" is placed in the definition of person, as signifying the singular in the genus of substance; and the term "rational nature" is added, as signifying the singular in rational substances.

Reply to Objection 1: Although this or that singular may not be definable, yet what belongs to the general idea of singularity can be defined; and so the Philosopher (De Praedic., cap. De substantia) gives a definition of first substance; and in this way Boethius defines person.

Reply to Objection 2: In the opinion of some, the term "substance" in the definition of person stands for first substance, which is the hypostasis; nor is the term "individual" superfluously added, forasmuch as by the name of hypostasis or first substance the idea of universality and of part is excluded. For we do not say that man in general is an hypostasis, nor that the hand is since it is only a part. But where "individual" is added, the idea of assumptibility is excluded from person; for the human nature in Christ is not a person, since it is assumed by a greater---that is, by the Word of God. It is, however, better to say that substance is here taken in a general sense, as divided into first and second, and when "individual" is added, it is restricted to first substance.

Reply to Objection 3: Substantial differences being unknown to us, or at least unnamed by us, it is sometimes necessary to use accidental differences in the place of substantial; as, for example, we may say that fire is a simple, hot, and dry body: for proper accidents are the effects of substantial forms, and make them known. Likewise, terms expressive of intention can be used in defining realities if used to signify things which are unnamed. And so the term "individual" is placed in the definition of person to signify the mode of subsistence which belongs to particular substances.

Reply to Objection 4: According to the Philosopher (Metaph. v, 5), the word "nature" was first used to signify the generation of living things, which is called nativity. And because this kind of generation comes from an intrinsic principle, this term is extended to signify the intrinsic principle of any kind of movement. In this sense he defines "nature" (Phys. ii, 3). And since this kind of principle is either formal or material, both matter and form are commonly called nature. And as the essence of anything is completed by the form; so the essence of anything, signified by the definition, is commonly called nature. And here nature is taken in that sense. Hence Boethius says (De Duab. Nat.) that, "nature is the specific difference giving its form to each thing," for the specific difference completes the definition, and is derived from the special form of a thing. So in the definition of "person," which means the singular in a determined "genus," it is more correct to use the term "nature" than "essence," because the latter is taken from being, which is most common.

Reply to Objection 5: The soul is a part of the human species; and so, although it may exist in a separate state, yet since it ever retains its nature of unibility, it cannot be called an individual substance, which is the hypostasis or first substance, as neither can the hand nor any other part of man; thus neither the definition nor the name of person belongs to it.

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod incompetens sit definitio personae quam boetius assignat in libro de duabus naturis, quae talis est, persona est rationalis naturae individua substantia.

Nullum enim singulare definitur. Sed persona significat quoddam singulare. Ergo persona inconvenienter definitur.

Argumentum 2

Praeterea, substantia, prout ponitur in definitione personae, aut sumitur pro substantia prima, aut pro substantia secunda.

Si pro substantia prima, superflue additur individua, quia substantia prima est substantia individua. Si vero stat pro substantia secunda, falso additur, et est oppositio in adiecto, nam secundae substantiae dicuntur genera vel species.

Ergo definitio est male assignata.

Argumentum 3

Praeterea, nomen intentionis non debet poni in definitione rei.

Non enim esset bona assignatio, si quis diceret, homo est species animalis, homo enim est nomen rei, et species est nomen intentionis. Cum igitur persona sit nomen rei (significat enim substantiam quandam rationalis naturae), inconvenienter individuum, quod est nomen intentionis, in eius definitione ponitur.

Argumentum 4

Praeterea, natura est principium motus et quietis in eo in quo est per se et non per accidens, ut dicitur in II physic..

Sed persona est in rebus immobilibus, sicut in deo et in Angelis. Non ergo in definitione personae debuit poni natura, sed magis essentia.

Argumentum 5

Praeterea, anima separata est rationalis naturae individua substantia. Non autem est persona.

Inconvenienter ergo persona sic definitur.

Corpus

Respondeo dicendum quod, licet universale et particulare inveniantur in omnibus generibus, tamen speciali quodam modo individuum invenitur in genere substantiae. Substantia enim individuatur per seipsam, sed accidentia individuantur per subiectum, quod est substantia, dicitur enim haec albedo, inquantum est in hoc subiecto. Unde etiam convenienter individua substantiae habent aliquod speciale nomen prae aliis, dicuntur enim hypostases, vel primae substantiae.

Sed adhuc quodam specialiori et perfectiori modo invenitur particulare et individuum in substantiis rationalibus, quae habent dominium sui actus, et non solum aguntur, sicut alia, sed per se agunt, actiones autem in singularibus sunt. Et ideo etiam inter ceteras substantias quoddam speciale nomen habent singularia rationalis naturae. Et hoc nomen est persona.

Et ideo in praedicta definitione personae ponitur substantia individua, inquantum significat singulare in genere substantiae, additur autem rationalis naturae, inquantum significat singulare in rationalibus substantiis.

Ad 1

Ad primum ergo dicendum quod, licet hoc singulare vel illud definiri non possit, tamen id quod pertinet ad communem rationem singularitatis, definiri potest, et sic philosophus definit substantiam primam.

Et hoc modo definit boetius personam.

Ad 2

Ad secundum dicendum quod, secundum quosdam, substantia in definitione personae ponitur pro substantia prima, quae est hypostasis.

Neque tamen superflue additur individua. Quia nomine hypostasis vel substantiae primae, excluditur ratio universalis et partis (non enim dicimus quod homo communis sit hypostasis, neque etiam manus, cum sit pars), sed per hoc quod additur individuum, excluditur a persona ratio assumptibilis; humana enim natura in christo non est persona, quia est assumpta a digniori, scilicet a verbo dei.

Sed melius dicendum est quod substantia accipitur communiter, prout dividitur per primam et secundam, et per hoc quod additur individua, trahitur ad standum pro substantia prima.

Ad 3

Ad tertium dicendum quod, quia substantiales differentiae non sunt nobis notae, vel etiam nominatae non sunt, oportet interdum uti differentiis accidentalibus loco substantialium, puta si quis diceret, ignis est corpus simplex, calidum et siccum, accidentia enim propria sunt effectus formarum substantialium, et manifestant eas. Et similiter nomina intentionum possunt accipi ad definiendum res, secundum quod accipiuntur pro aliquibus nominibus rerum quae non sunt posita. Et sic hoc nomen individuum ponitur in definitione personae, ad designandum modum subsistendi qui competit substantiis particularibus.

Ad 4

Ad quartum dicendum quod, secundum philosophum, in V metaphys., nomen naturae primo impositum est ad significandam generationem viventium, quae dicitur nativitas. Et quia huiusmodi generatio est a principio intrinseco, extensum est hoc nomen ad significandum principium intrinsecum cuiuscumque motus.

Et sic definitur natura in II physic..

Et quia huiusmodi principium est formale vel materiale, communiter tam materia quam forma dicitur natura. Et quia per formam completur essentia uniuscuiusque rei, communiter essentia uniuscuiusque rei, quam significat eius definitio, vocatur natura. Et sic accipitur hic natura.

Unde boetius in eodem libro dicit quod natura est unumquodque informans specifica differentia, specifica enim differentia est quae complet definitionem, et sumitur a propria forma rei. Et ideo convenientius fuit quod in definitione personae, quae est singulare alicuius generis determinati, uteretur nomine naturae, quam essentiae, quae sumitur ab esse, quod est communissimum.

Ad 5

Ad quintum dicendum quod anima est pars humanae speciei, et ideo, licet sit separata, quia tamen retinet naturam unibilitatis, non potest dici substantia individua quae est hypostasis vel substantia prima; sicut nec manus, nec quaecumque alia partium hominis. Et sic non competit ei neque definitio personae, neque nomen.