We have now completed our historical survey. It would be possible to carry the story further, for the decades after the hesychast controversy saw a substantial interest in Aquinas among the Byzantines. The Summa Contra Gentiles was translated into Greek in 1355, and other works, including the Summa Theologiae, soon followed. They provoked a lively controversy, with a small but vigorous minority (led by the translators, Demetrius and Prochorus Cydones) seeking to persuade their countrymen of the merits of Thomism. This sudden expansion of horizons contributed to the turbulence of Byzantine intellectual life in its final days, helping make possible the originality of men like Gemisto Plethon and Cardinal Bessarion, who initiated the revival of Platonism in the Renaissance. No doubt it was the Byzantines' growing sense of desperation that opened their minds to the possibility that they might have something to learn from the West.

What has Athens to do with Jerusalem? That is a question that no student of western culture can avoid. Tertullian, who first posed it, did so in the course of accusing philosophy of engendering heresy. The implication behind his question was that Athens and Jerusalem are two different worlds, and therefore categories deriving from Greek thought should have no place within the Christian faith. Yet even Tertullian found it impossible in practice to maintain such a strict division. The Church as a whole tended instead to follow the lead of the Greek apologists, who had drawn freely on Greek philosophy in interpreting the Christian message. Ultimately the many forms of Christian thought that vied for pre-eminence throughout the Middle Ages and Renaissance, and into the early modern era, almost invariably owed much to both of Tertullian's opposing worlds. The result is that Athens and Jerusalem have been deeply and inextricably intertwined in the formation of western culture.

This fusion gives to Tertullian's question a different and more alarming meaning. Viewed in light of the intervening history, the question is not simply whether Christian theology should make use of Greek philosophy; it is whether the two great sources of our civilization are compatible. To hold that they are not is necessarily to put into question, not only at least one of them (and perhaps both), but also the civilization that grew out of their union.

The eastern tradition as we have presented it so far is rich but polyphonic. One finds terms as fundamental as energeia and “the things around God” being used differently by different authors, and concepts such as ceaseless prayer and the uncreated light achieving great importance without any attempt to incorporate them into a dogmatic synthesis. No doubt part of the reason was the strong sense of unanimity within the tradition as a whole. There was never any sudden loss of texts, or division into schools, or rise of a scholastic method – all factors that, had they occurred, would have encouraged authors to look for shortcomings within the tradition and to emphasize their own originality. The Byzantines took for granted that what had been said by the Fathers was correct and complete, and they saw their own task as that of applying this inherited wisdom to the issues at hand. Consequently, even a step of great originality was rarely heralded as such. Behind this conservatism there lay also a deeper cause, namely the apophaticism at the root of the entire tradition. What is the point of spinning out words about God when He can be known only through practice? On such a view theology, however complex it may become, is ultimately simply the enterprise of preserving “the faith once delivered to the saints.”

With Plotinus (c. 205–270) we are again in the presence of a philosophical mind of the first rank. Plotinus is conventionally regarded as the founder of Neoplatonism, and it is certainly true that he looks to Plato for inspiration more than to any other philosopher. But scholars have long recognized that in many ways he is as much indebted to Aristotle as to Plato. Something of Plotinus' attitude to Aristotle emerges in the following passage of the Life of Plotinus by Porphyry, who was Plotinus' student and an important philosopher in his own right.

As A. H. Armstrong remarks in a note on this passage, it “shows clearly how scholarly and professional a philosopher Plotinus was and how he worked, though with great originality, on the basis of an extensive school tradition.”

The history of Christian thought in the East after Dionysius is often presented as a series of controversies: the Christological controversies, the iconoclast controversy, the filioque controversy, the hesychast controversy. Although this approach works well for describing the growth of Christian doctrine, it is less suited to uncovering the philosophical presuppositions that shaped the eastern Christian worldview. The question of where philosophy ends and theology begins within the eastern context is not one that has an easy answer, nor do we need to settle it here. It is sufficient to note that there are recognizable philosophical issues on which the authors of this period have a great deal to say: issues such as the status and meaning of nature; the relationship between body and soul, and the sensible and the intelligible; the way in which symbols and images represent their prototypes; the interconnection of theory and practice; person as a category irreducible to nature; and, above all, the nature of God and the possibility of human communion with the divine. On such topics the thought of the Christian East is best approached, not in terms of doctrinal history, but as the gradual working out of the fundamental revision of Neoplatonism begun by the Cappadocians and Dionysius.

In this chapter our aim is not to present a comprehensive history of eastern Christian thought even in its philosophical dimension. The thread we are tracing is energeia.

Although Aristotle never takes credit for coining the word energeia, there can be little doubt that it was his own invention. It appears nowhere in extant Greek literature prior to Aristotle, and even for some decades after his death it is restricted mainly to philosophical writers, particularly those of Aristotle's own school. By contrast, it occurs 671 times in Aristotle's works, about once for every other page of the Berlin edition. Unfortunately Aristotle discusses its etymology only once, remarking briefly that energeia is derived from “deed” or “thing done” (τὸ ἔργον) (Met. ix.8 1050a22). Although this gives us the ultimate source of the term, the combination of en with ergon already had precedents in Greek, and it is likely that one of these was the more proximate source. The two available candidates are energos, an adjective meaning “active, effective,” and energein, a verb meaning “to be active or effective, to operate.” In either case the root sense of energeia is something like “activity, operation, or effectiveness.” To say more than this based on etymology would be rash.

One way to proceed at this point would be to list its various meanings in dictionary fashion, illustrating each by representative texts. Such a procedure would not explain what united the various meanings in Aristotle's mind and why he believed it appropriate to use the same term for them all. It would thus risk missing the term's more subtle nuances.

The story of the diffusion of Aristotelianism during the centuries after Aristotle's death is a long and tangled one. The works making up the Corpus Aristotelicum as we know it seem to have originated as notes written for lectures to students in the Lyceum. Aristotle also wrote a number of more popular works, the so-called “exoteric” writings which today survive only in fragments. Among these is the Protrepticus, whose treatment of energeia was discussed in Chapter 1. There is general agreement that the exoteric works were in circulation during the Hellenistic period, and that as late as the second century a.d. they still formed the main basis for the educated public's understanding of Aristotle. The fate of the school treatises is more obscure. According to a story told by Strabo and Plutarch, “Aristotle's books” passed at his death into the hands of Theophrastus, Aristotle's student and colleague, and the second head of the Lyceum. Theophrastus in turn bequeathed them to Neleus of Skepsis, who removed them to his hometown. There they languished in obscurity until they were recovered toward the end of the second century b.c. by Apellicon, a bibliophile who brought them to Athens. He published a faulty and apparently little noticed edition. Finally, about the middle of the first century b.c., a corrected edition was published by a professional Aristotelian scholar named Andronicus of Rhodes. All subsequent manuscripts of the school treatises ultimately rely on this Andronican edition.

After the death of Plotinus the mantle of leadership among Platonists passed to his former student, Porphyry (232–c. 305). It has long been recognized that Porphyry played a major role in the formation of Neoplatonism in the western half of the Empire. Augustine, for example, discusses his views at length in Book x of The City of God, and Boethius relies on him heavily in the interpretation of Aristotle's logic. One of Porphyry's most influential acts was to write a commentary on the Chaldaean Oracles, an obscure piece of religio-philosophical verse dating from the middle of the second century. By doing so he brought into the orbit of Neoplatonism the system of ritualized interaction with the gods known as theurgy. Porphyry himself had strong doubts about theurgy; he regarded it as at best a useful way of cleansing the soul, one merely preparatory for the only true salvation, which is achieved through philosophy. But his student Iamblichus rose to its defense, and this quarrel between Porphyry and Iamblichus marked a major parting of the ways in the early history of the school. Iamblichus' writings ultimately became definitive for Neoplatonism in the eastern half of the Empire, whereas they remained virtually unknown in the West.

In this chapter we will examine Porphyry and other Neoplatonists of the West. Part of our story will be that of how energeia as it is found in Plotinus and Porphyry was transformed into the medieval (and especially Thomistic) concept of esse, the “act of being.”

Most of the texts discussed in the previous chapter remained unknown to the West during the Middle Ages. It is not surprising that the magical papyri, Hermetica, and works of Iamblichus and Proclus went untranslated; rather more surprising is that the same is true of the works of Justin Martyr, Athenagoras, Clement, Origen, and Athanasius, with the exception of Origen's De Principiis and some exegetical treatises. All told, of the works we have discussed the only one that played a role in the formative stages of western thought was the New Testament, which of course was available in the Vulgate of Jerome. There we find energeia translated as operatio and energein as operari. Although these renderings were probably the best available, they do not possess the same fluidity of meaning as the original. To think of the divine operationes as forces or active powers that can be shared in by human activity would not normally occur to a Latin reader. This is not only because the major works in which the expansion of meaning took place were not translated into Latin; it is also because operatio does not share the association of energeia with actuality, much less with the fusion of activity and actuality that we have traced in earlier chapters. That is why, when the works of Aristotle were translated in the twelfth and thirteenth centuries, energeia had to be rendered in different contexts by three different terms: operatio, actus, and actualitas.

Up to this point we have traced two broad strands in the development of Aristotle's thought on energeia. Both take their beginning from his early use of the term to mean the active exercise of a capacity as distinct from mere possession of that capacity. In one strand we find Aristotle purifying energeia from its early associations with motion or change (κίνησις), distinguishing it as that type of activity that contains its own end and hence is not constrained to unfold through a temporal process. The other strand is rooted in the early distinction between energeia and dunamis in the sense of capacity. As Aristotle broadens dunamis to encompass all types of potency, he correspondingly broadens energeia to encompass all types of actuality. As we have seen, he goes on to argue that actuality is prior to potentiality in a number of respects, of which the most important is priority in substance. His argument for this latter claim hinges on the view that things existing eternally and of necessity, such as the stars and planets, are free of potency in respect to existence. There is thus an intimate link between eternity and necessity, on the one hand, and actuality on the other.

That link becomes a central theme of Metaphysicsxii.6–10, Aristotle's only sustained discussion of the Prime Mover.

In his commentary on Aristotle's de Interpretatione Ammonius asks ‘among which of the things that are in any way one should look for truth and falsehood’ (17, 29–30). In Aristotle's works there is no formulation of this or of an equivalent question. So, there is a case for doubting that Aristotle ever addressed the problem of what items are bearers of truth or falsehood. However, even if Aristotle never addressed this problem, it is still worthwhile considering what the items are which Aristotle does in fact speak of as true or false. For this result will provide a useful indication for determining what solution Aristotle would have offered for the problem of what items are bearers of truth or falsehood, had he addressed it.

Aristotle applies the word ‘true’ (‘ἀληθής’) and its cognates to items of three main kinds: objects (which include states of affairs), mental items (states or acts of believing, knowing, grasping by means of the intellect, perceiving, imagining, etc.), and linguistic items (sentences).

Section 1 of this chapter focuses on objects, in particular on states of affairs. I examine two passages from the Metaphysics. The first, which constitutes the beginning of Δ 29, is the most unequivocal testimony of Aristotle's commitment to states of affairs (I devote some arguments to showing that it is really states of affairs Aristotle is concerned with). The second Metaphysics passage is the first part of Θ 10. Aristotle describes states of affairs as being true or false in the strictest, i.e. most fundamental, sense because their truth and falsehood is appealed to in explaining the truth and falsehood of items of other types: an affirmative predicative belief or sentence is true (false) when and only when the state of affairs it concerns is true (false), while a negative predicative belief or sentence is true (false) when and only when the state of affairs it concerns is false (true).

The two-place relations involved in the truth conditions for quantified assertions. An important feature of [17], the definition of truth for predicative assertions I attribute to Aristotle, is that the truth conditions for (those utterances which are) quantified predicative assertions involve two-place relations (the combination of universally holding, the division of universally failing to hold, the combination of not universally failing to hold, and the division of not universally holding) obtaining between the universals signified by the predicates and the subjects of the assertions. These two-place relations are to some extent reflected in views formulated in the logical writings of Aristotle himself and of some of his pupils.

1. The expression ‘to hold universally’. In some passages Aristotle uses the expression ‘to hold universally’ (‘καθόλου ὑπάρχειν’) to express a relation which is at least close to the combination of universally holding. This fits well with the part of [17] which concerns universal affirmative predicative assertions.

2. Universal affirmative predicative assertions and being a part of a whole. At the beginning of the Prior Analytics Aristotle says that he intends to determine ‘what it is for this to be, or not to be, in this taken as a whole [ἐν ὅλῳ εἶναι ἢ μὴ εἶναι τόδ∊ τῷδε]’ (1.1, 24a13–14). Aristotle probably wants to describe what universal affirmations and denials say.

This chapter examines what truth conditions for predicative assertions Aristotle is committed to.

Section 1 addresses a preliminary issue: Aristotle's conception of universals. Universals are neither concepts nor linguistic expressions: rather, universals are objects whose nature is neither mental nor linguistic. A universal is an object which is predicated of many things, an individual is an object which is not predicated of many things.

Sections 2–4 concentrate on the truth conditions for singular and quantified predicative assertions (evidence is mainly provided by passages from de Interpretatione). Section 2 addresses the discussion of truth and falsehood in de Interpretatione 1, where Aristotle alludes to the theory of Metaphysics Ε 4: in an affirmative (negative) predicative belief one object is joined with (separated from) one object. The bulk of section 2 is taken up by a discussion of two objections that could be raised against connecting de Interpretatione 1 with Metaphysics Ε 4. Section 3 addresses Aristotle's theory of assertions. Not every sentence is true or false (prayers are neither), and every sentence that is true or false is an assertion (the converse fails). Every affirmative predicative assertion asserts something ‘about’ something, every negative predicative assertion asserts something ‘away from’ something. The operation of asserting-about (asserting-away-from) performed by an affirmative (negative) predicative assertion is the linguistic counterpart of the operation of joining (separating) performed in an affirmative (negative) predicative belief. In both cases the operations are performed on objects (not on linguistic expressions or on thoughts).

Is Aristotle coherent? Aristotle's position in Int. 9 has been taken to be incoherent. For Aristotle accepts Excluded Middle (which involves endorsing every instance of ‘α ∨ ¬α’) but denies Bivalence (which involves denying that at every time every assertion is either true or false). It is hard to see how this could be coherent – but the following formal semantic theory shows that it is.

Expanded semantic theory Appendix 5 contained a formal presentation of a semantic theory for a fragment of natural language that includes some present-tense predicative assertions. Here, in appendix 6, this semantic theory is expanded. The expanded semantic theory covers a slightly larger fragment of natural language, a fragment including not only some present-tense predicative assertions, but also some past- and future-tense predicative assertions, some ‘tomorrow’-assertions (i.e. predicative assertions that begin with an utterance of the phrase ‘tomorrow it will be the case that’), and some negative and disjunctive assertions.

Expansion of the alphabet The alphabet of the semantic theory presented in appendix 5, described in [54] and [55], must be expanded.