secunda pars incipit ibi: amplius autem etc.
and he begins the second part at further, it must extend (1098a18; ).
Primo igitur accipit ex praemissis quod proprium opus hominis sit operatio animae quae est secundum ipsam rationem vel non sine ratione, quod dicit propter operationem appetitus regulati ratione. Hoc autem in omnibus communiter invenitur quod idem est opus alicuius rei in genere acceptae et opus illius rei si sit bona, nisi quod oportet apponere ex parte operationis id quod pertinet ad virtutem, sicut opus citharistae est citharizare, opus autem boni citharistae est bene citharizare et similiter est in omnibus aliis.
First, then, we know from the premises  that the proper function of a man is a psychic activity in accord with reason itself or at least not independent of reason. The latter is mentioned because of the activity of the appetite controlled by reason. Now, as a rule, we find that the function of a thing generally and the efficient activity of that thing are of the same nature, except that allowance must be made for the part played by skill. For example, the function of a harpist is to play the harp, and the function of a good harpist is to play the harp well. The same is true of all other functions.
128. Si igitur opus hominis consistit in quadam vita prout scilicet homo operatur secundum rationem, sequitur quod boni hominis sit bene operari secundum rationem et optimi hominis, scilicet felicis, optime hoc facere. Sed hoc pertinet ad rationem virtutis quod unusquisque habens virtutem secundum eam bene operetur, sicut virtus equi est secundum quam bene currit. Si ergo operatio optimi hominis, scilicet felicis, est ut bene et optime operetur secundum rationem, sequitur quod humanum bonum, scilicet felicitas, sit operatio secundum virtutem, ita scilicet quod si est una tantum virtus hominis, operatio quae est secundum illam virtutem erit felicitas, si autem sunt plures virtutes hominis, erit felicitas operatio quae est secundum optimam illarum, quia felicitas non solum est bonum hominis, sed optimum.
128. If, therefore, man’s proper role consists in living a certain kind of life—namely, according to the activity of reason—it follows that it is proper to a good man to act well according to reason, and to the very good man or the happy man to do this in superlative fashion. But this belongs to the nature of virtue that everyone who has virtue should act well according to it, as a horse with good training or “virtue” should run well. If, then, the activity of the very good man or the happy man is to act well—in fact, to act to the best of his ability according to reason—it follows that the good of man, which is happiness, is an activity according to virtue. If there is only one virtue for man, his activity according to that virtue will be happiness. If there are a number of such virtues for man, happiness will be the activity according to the best of them. The reason is that happiness is not only the good of man but the best good.
129. Deinde cum dicit: amplius autem in vitam perfectam etc., investigat aliam differentiam felicitatis. Requiritur enim ad felicitatem continuitas et perpetuitas quantum possibile est; hoc enim naturaliter appetitus habentis intellectum desiderat utpote apprehendens non solum esse ut nunc, sicut sensus, sed etiam esse simpliciter; cum autem esse sit secundum se ipsum appetibile, consequens est quod, sicut animal per sensum apprehendens esse ut nunc appetit nunc esse, ita etiam homo per intellectum apprehendens esse simpliciter appetit esse simpliciter et semper et non solum ut nunc; et ideo de ratione perfectae felicitatis est continuitas et perpetuitas. Quam tamen praesens vita non patitur, unde in praesenti vita non potest esse perfecta felicitas. Oportet tamen quod felicitas qualem possibile est esse praesentis vitae sit in vitam perfectam, id est per totam hominis vitam. Sicut enim una hirundo veniens non demonstrat ver nec una dies temperata, ita etiam nec una operatio semel facta facit hominem felicem, sed quando homo per totam vitam continuat bonam operationem.
129. Then, at further, it must extend (1098a18), he inquires into the other specific difference of happiness. Continuity and perpetuity, to some extent, are also required for happiness. These qualities are naturally desired by the appetite of a person endowed with reason, who apprehends not a particular being, as our senses do, but also being in itself. Now, being is of itself desirable. It follows, then, that, as an animal that apprehends a particular being by its senses desires that particular being, so also man, apprehending being in itself, desires it as always existing and not this particular being alone. So continuity and perpetuity, which are not found in the present life, belong to the nature of perfect happiness. Hence, perfect happiness cannot be had in this life. However, the happiness attainable here must extend to a complete life—that is, through the whole life of man. As the sight of a single swallow or one clear day does not prove that spring is here, so a single good deed is not enough to make a man happy. It arises rather from the continued performance of good deeds throughout his whole life.
130. Sic ergo patet quod felicitas est operatio propria hominis secundum virtutem in vitam perfectam.
130. From this discussion, therefore, it is clear that happiness is a virtue-oriented activity proper to man in a complete life.
The Task Before Us
Circumscribatur quidem igitur bonum ita. Oportet enim forte figuraliter dicere primum, deinde posterius rescribere. 
In this way, therefore, the good of happiness has been sketched, for the proper procedure is first to study a subject according to its general notions and afterward to explain it more fully. 
Videbitur autem utique hominis esse perducere et particulatim disponere quae bene habentia circumscriptione. 
It would indeed seem a reasonable mode of procedure to make a sketch of the matter and then to investigate its features one by one. 
Et tempus talium inventor vel cooperator bonus esse. Unde et artium facta sunt additamenta; omnis enim est apponere quod deficit. 
In this matter, time seems to be, as it were, a good discoverer and a special assistant. Thus, improvements in the arts have been due to successive artists, each making his own contribution. 
Meminisse autem et praedictorum oportet, et certitudinem non in omnibus similiter exquirere, sed in singulis secundum subiectam materiam et in tantum in quantum proprium est doctrinae. 
We must recall what was said before, that the same certitude is not to be expected in all sciences, but in each according to the subject matter, and that the degree of certitude should be suited to the subject taught. 
Et enim tector et geometra differenter inquirunt rectam. Hic quidem enim in quantum utilis est ad opus, hic autem quid est vel quale quid, speculator enim est veri. Secundum eundem utique modum et in aliis est faciendum ut non quae extra opera operibus plura fiant. 
For a carpenter and a geometrician both study a straight line, but for different reasons. The carpenter does so to the extent that this is useful in his work; the geometrician, as a student of truth, wants to learn what a line is and how it differs from other figures. This distinction must be observed in other practical sciences lest they be burdened with discussions that are out of place. 
Non expetendum autem neque causam in omnibus similiter, sed sufficiens in quibusdam hoc quoniam demonstrari bene, utputa circa principia; hoc autem, quia primum et principium. Principiorum autem haec quidem inductione contemplata sunt, haec vero sensu, haec autem consuetudine quadam et alia autem aliter. 
Likewise, we must not seek causes equally in all matters, but in some it suffices to establish a fact. This is the case with the first principles of a science, since a principle is a starting point. Now, we understand some principles by induction, some by observation, some by custom, and others in other ways. 
Pertransire autem oportet tentare singula secundum quod innata sunt et studendum qualiter terminentur bene. Magnum enim habent auxilium ad sequentia; videtur enim plus quam dimidium totius esse principium et multa manifesta fieri per ipsum eorum quae quaeruntur. 
In all cases, we must strive for a thorough knowledge of each set of principles according to their nature and must study how to define them properly. Principles are a great help in understanding what follows. Indeed, a single principle seems to be more than half of the whole, for it furnishes answers to many of our questions. 
131. Circumscribatur quidem igitur bonum etc. Postquam Philosophus investigavit diffinitionem felicitatis, nunc ostendit quid post hoc agendum relinquatur. Et circa hoc duo facit:
131. In this way, therefore. After the Philosopher has investigated the definition of happiness itself, he now shows in a twofold fashion what may still remains to be done.
primo ostendit quid restat agendum;
He indicates first what remains to be done;
secundo quomodo id agere oporteat, ibi: meminisse autem et praedictorum oportet etc.
second, at we must recall (1098a26; ), how this should be done.
Circa primum tria facit.
In regard to the initial point, he does three things.
Primo proponit quid sit factum et quid restet agendum. Et dicit quod ita sicut supra habitum est circumscribitur bonum finale hominis quod est felicitas. Et vocat circumscriptionem notificationem alicuius rei per aliqua communia quae ambiunt quidem ipsam rem, non tamen adhuc per ea in speciali declaratur natura illius rei. Quia, ut ipse subdit, oportet quod aliquid primo dicatur figuraliter, id est secundum quandam similitudinariam et extrinsecam quodam modo descriptionem, et deinde oportet ut manifestatis quibusdam aliis resumatur illud quod fuit prius figuraliter determinatum et sic iterato plenius describatur. Unde et ipse postmodum in fine libri de felicitate tractatum complebit.
First, he manifests what has been done and what remains to be done. He says that the final good of man, which is happiness, has been previously sketched [103–130]. By “a sketch,” he means the knowledge acquired through some common principles, which indeed gives a picture of the matter, but not in such a way that the nature of that thing in particular is manifested. The reason for this is, as he himself says, that a thing should first be studied according to its general characteristics—that is, by a general description that is like it and in a way extrinsic to it. Then, with other matters clarified, we must take up what was previously sketched roughly and etch in the lines more sharply. For this reason he himself will take up in greater detail the treatise on happiness toward the end of this work.
132. Secundo ibi: videbitur autem utique etc., assignat rationem eius quod dictum est. Hoc enim ad naturam cuiuslibet hominis pertinere videtur ut ea quae bene continent descriptionem alicuius rei perducat, scilicet de imperfecto ad perfectum, et particulatim disponat, primo scilicet unam partem et postea aliam investigando. Ad hominis enim naturam pertinet ratione uti ad veritatis cognitionem; rationis autem proprium est ab uno in aliud procedere, intellectus autem proprium est statim apprehendere veritatem; et ideo ad hominem pertinet ut paulatim in cognitione veritatis proficiat, substantiae vero separatae quae intellectuales dicuntur statim absque inquisitionem notitiam veritatis habent.
132. Second, at it would indeed seem (1098a22), he assigns the reason for the statement just made , saying that it seems natural for man to advance from the imperfect knowledge that covers a good description of things to a perfect knowledge of them by filling in the details. This he does by investigating first one part and then another, for it is according to man’s nature to proceed by the steps of reason to a knowledge of the truth. Reason has this peculiar characteristic, that it grasps the truth gradually, and as a consequence, man properly perfects himself in knowledge little by little. On the contrary, separated or intellectual substances attain at once to the knowledge of the truth without any such investigation.
133. Tertio ibi: et tempus talium etc., ostendit per quid homo ad praedicta iuvetur. Et dicit quod eorum quae bene se habent ad aliquid circumscribendum, videtur tempus esse quasi adinventor vel bonus cooperator, non quidem quod tempus per se ad hoc aliquid operetur, sed secundum ea quae in tempore aguntur. Si enim aliquis tempore procedente det se studio investigandae veritatis, iuvatur ex tempore ad veritatem inveniendam, et quantum ad unum et eumdem hominem qui postea videbit quod prius non viderat, et etiam quantum ad diversos utpote cum aliquis intuetur ea quae sunt a praedecessoribus adinventa et aliquid superaddit. Et per hunc modum facta sunt additamenta in artibus quarum a principio aliquid modicum fuit adinventum et postmodum per diversos paulatim profecit in magnam quantitatem, quia ad quemlibet pertinet superaddere id quod deficit in consideratione praedecessorum.
133. Third, at in this matter time (1098a23), he shows how a man may be helped in this procedure. He says that time seems to be, as it were, a discoverer of things well suited to sketch a subject and to be of special assistance in the work. The meaning is not that time itself contributes anything, but that this help comes with time. If someone should busy himself investigating the truth for a period, he will be aided in the discovery of the truth by the passage of time. This is true in the case of the same person who will understand subsequently what he had not understood before, and also for different persons, as in the case of a man who learns the things discovered by his predecessors and adds something himself. In this way improvements have been made in the arts, in which a small discovery was made first and afterward notable advances were made by the efforts of various men, each looking upon it as a duty to supply what is lacking in the knowledge of his predecessors.
134. Si autem e contrario exercitium studii praetermittatur, tempus est magis causa oblivionis, ut dicitur in IV Physicorum, et quantum ad unum hominem, qui si se negligentiae dederit obliviscetur quod scivit, et quantum ad diversos, unde videmus multas scientias vel artes quae apud antiquos viguerunt paulatim cessantibus studiis in oblivionem abiisse.
134. But if, on the contrary, application to study be neglected, time is rather a cause of forgetfulness, as is said in Physics 4. We see indeed that the negligent individual forgets what he knows, and in human history we observe that many sciences that flourished among the ancients gradually have been lost when interest in them ceased.
135. Deinde cum dicit: meminisse autem et praedictorum etc., ostendit quomodo sit prosequendum id quod restat.
135. Then, at we must recall (1098a26), he shows how we must follow up the remainder of our task.
Et primo proponit hoc in generali, reducens ad memoriam ea quae supra in prooemio dicta sunt, quod scilicet non oportet similiter exquirere certitudinem in omnibus, sed in singulis secundum convenientiam materiae, prout scilicet est proprium illi doctrinae quae circa illam materiam versatur.
First, he presents this in general by recalling to mind what was said in the introduction [32, 36], that we must not look for the same certitude in all subjects, but in each according to the matter, namely, that which is proper to the subject taught.
136. Secundo ibi: et enim tector et geometra etc., manifestat quod dixerat in speciali.
136. Second, at for a carpenter (1098a29), he makes specific what he has said.
Et primo quantum ad id quod diversimode in diversis observari oportet;
First, he takes up what must be handled differently for different subjects,
secundo quantum ad id quod communiter in omnibus observandum est, ibi: pertransire autem oportet etc.
and second, at in all cases we must (1098b4; ), what must be observed generally in all subjects.
Circa primum tradit duplicem diversitatem.
In regard to the first, he gives a threefold difference.
Quarum prima est secundum differentiam scientiae practicae et speculativae. Unde dicit quod tector, id est artifex operativus, et geometra, qui est speculativus, differenter inquirunt de linea recta. Artifex quidem operativus, utpote carpentarius, inquirit de linea recta quantum est utile ad opus, utpote ad secandum ligna vel aliquid aliud huiusmodi faciendum; sed geometra inquirit quid est linea recta et quale quid sit, considerando proprietates et passiones ipsius, quia geometra intendit solam speculationem veritatis. Et secundum hunc modum faciendum est in aliis scientiis operativis, ut non sequatur hoc inconveniens ut in scientia operativa fiant plures sermones ad opera non pertinentes illis sermonibus qui sunt circa opera, puta, si in hac scientia morali aliquis vellet pertractare omnia quae pertinent ad rationem et alias partes animae, oporteret plura de hoc dicere quam de ipsis operibus. Est enim in unaquaque scientia vitiosum ut homo multum immoretur in his quae sunt extra scientiam.
The first of these is the difference between a practical and a speculative science. He says, therefore, that a carpenter, who is a practical man, and a geometrician, who is a theorist, study a straight line for different reasons. A practical man—a carpenter—studies a line insofar as it is useful for his work in sawing wood or in doing anything else of this nature. But the geometrician investigates what a line is—its qualities and its nature—by considering the properties and potentialities. He is interested only in the study of truth. We must proceed in the first way to avoid many discussions that are out of place in practical sciences. For instance, in moral matters, we must steer clear of an exhaustive treatment of the intellect and the other powers of the soul to the neglect of the study of human acts themselves. It is a serious defect in any science to squander time on matter outside the science.
137. Aliam autem diversitatem tangit ibi: non expetendum autem etc. Quae attenditur secundum differentiam principiorum et eorum quae sunt ex principiis. Et dicit quod non est in omnibus eodem modo causa inquirenda, alioquin procederetur in infinitum in demonstrationibus, sed in quibusdam sufficit quod bene demonstretur, id est manifestetur, quoniam hoc ita est, sicut in his quae accipiuntur in aliqua scientia ut principia; quia principium oportet esse primum, unde non potest resolvi in aliquid prius. Ipsa autem principia non omnia eodem modo manifestantur, sed quaedam considerantur inductione, quae est ex particularibus imaginatis, sicut in mathematicis, puta quod omnis numerus est par aut impar; quaedam vero accipiuntur sensu, sicut in naturalibus, puta quod omne quod vivit indiget nutrimento; quaedam vero consuetudine, sicut in moralibus, utpote quod concupiscentiae diminuuntur si eis non obediamus; et alia etiam principia aliter manifestantur, sicut in artibus operativis accipiuntur principia per experientiam quamdam.
137. He treats a second difference at likewise, we must not (1098a34; ). Here he considers the difference between principles and deductions made from them. He says that the cause is not to be sought equally in all matters; otherwise, we would proceed to infinity in demonstrating. But in some cases it is sufficient to show clearly that a thing is so. This is true of principles that are taken for granted in a science, since they are the beginning and cannot be reduced to anything previous. Now, principles themselves are not manifested in the same way. But some are understood by induction from particular examples, such as that every number is even or odd. Some are taken from observation, such as that, in nature, every living thing needs nourishment. Some are taken from custom, such as that, in morals, sensual desires are diminished if we do not give in to them. Still other principles are manifested in still other ways, such as that, in the practical arts, principles are learned by a sort of experience.
138. Deinde cum dicit: pertransire autem oportet etc., determinat modum quantum ad id quod est communiter observandum in omnibus. Et dicit quod homo debet insistere ad hoc quod singula principia pertranseat, scilicet eorum notitiam accipiendo et eis utendo, secundum quod nata sunt cognosci; et studendum qualiter determinentur in hominis cognitione, ut scilicet sciat distinguere principia ab invicem et ab aliis. Cognitio enim principiorum multum adiuvat ad sequentia cognoscenda; principium enim videtur plus esse quam dimidium totius, quia scilicet omnia alia quae restant continentur virtute in principiis, et hoc est quod subdit, quod per unum principium bene intellectum et consideratum multa fiunt manifesta eorum quae quaeruntur in scientia.
138. Then, at in all cases, we must (1098b4), he sets down the procedure to be followed generally in all such matters. He says that a person ought to persist in going over thoroughly each set of principles, both speculatively and practically, in the way a knowledge of their nature demands and in studying how men understand them. Thus, a man will learn how to distinguish one principle from another, and one set of principles from another set. A knowledge of principles is a great help in understanding the conclusions that flow from them. Indeed, a single principle seems to be more than half of the whole, since the content of a science is contained in the principles. He adds that many answers we look for in a science are clear from one principle well understood and completely thought out.
Confirmation of the Definition
Scrutandum ergo de ipso non solum ex conclusione et ex quibus sermo, sed et ex dictis de ipso. Vero quidem enim omnia consonant existentia, falso autem cito dissonat verum. 
In our study of the principles, we must carefully examine not only the conclusions and the premises from which the argument proceeds, but also the considered views of others. Everything indeed will fall into agreement with what is true, and the truth will be quickly seen to be at variance with the false. 
Divisis itaque bonis tripliciter et his quidem exterius dictis, his autem circa animam et corpora, circa animam principalissime dicimus et maxime bona. Actus autem et operationes animales circa animam ponimus. Quare bene utique dicetur secundum hanc opinionem antiquam existentem et confessam a philosophis. 
Goods have been classified as external, of the soul, and of the body. Among these, we hold that the goods of the soul are the best and most properly called goods. We attribute vital actions and operations to the soul. Therefore, our opinion must be sound, for it is in agreement with that ancient one held by the philosophers. 
Recte autem et quoniam actus quidam dicuntur et operationes finis. Ita enim eorum quae circa animam sunt bonorum fit, et non eorum quae exterius. 
It was stated accurately, then, that we identify the end with certain acts and operations. Thus, happiness will be accounted one of the goods of the soul, and not an external good.