Brentano and Aristotle on the Ontology of Intentionality

Final version in: Denis Fisette / Guillaume Fréchette (eds.), Themes from Brentano, Amsterdam: Rodopi 2013. Brentano and Aristotle on the Ontology of Intentionality Arkadiusz Chrudzimski (Salzburg and Szczecin) It is often claimed that Brentano’s rediscovery of intentionality has been strongly influenced by Aristotle. Brentano himself stressed repeatedly his affinity to Aristotle1 and this selfinterpretation was by no means restricted to the theory of intentionality. In fact, Brentano seemed to believe that almost all of what he had discovered during his most influential years (1874–1895) has its more or less remote roots in the philosophy of Aristotle.2 Yet if we carefully compare the picture of intentionality that is to be found in Aristotle’s De Anima with Brentano’s theory of immanent objects, we find more differences than similarities. The truth is that Brentano developed a quite different ontology of intentionality, and his references to Aristotle should be seen as a conventional homage to his master rather than as something of substance that could help us to understand better Brentano’s own theory. What Brentano in fact took from Aristotle was rather his way of doing philosophy and certain isolated ideas, but certainly not theories in their entirety.3 1. The theory of immanent object In this section, I am going to sketch Brentano’s theory of intentionality insofar as it introduces immanent objects as a special kind of ontological category. But, strictly speaking, there is no single theory of intentionality in Brentano. It is well known that the late Brentano (after 1904) rejected immanent objects understood as a special ontological category as well as all entities that did not belong to the category of things, but the young Brentano (1862–1874) was also typically very far from such ontological extravagances as to regard intentional objects as a kind of special category. In formulating his early theory of intentionality, he often referred to the Scholastic, mainly Scottist, tradition and its theory of the ens objectivum. According to 1 Cf. e.g. Brentano 1874/1924, p. 124 f.; Brentano 1982, p. 26. 2 Cf. e.g. his frequently cited letter, in: Brentano 1977, p. 291. 3 This is true even of Brentano’s early metaphysics, as developed in his Lectures on Metaphysics from 1867 (manuscript M 96). Cf. Chrudzimski 2004, Chapter 3 and Chrudzimski/Smith 2004, pp. 197–204. 1 this tradition, when a conscious subject is thinking of an object, he can be said to have this object objectively in his mind. But such a reference to an “objective mode of being” was intended to have no ontological consequences.4 It is not excluded that even in the Psychology from an Empirical Point of View (1874) – a book considered to be the locus classicus of the theory of immanent objects – the notion of “having something immanently as an object”5 is still to be interpreted in the same ontologically neutral fashion.6 Nonetheless, Brentano’s manuscripts provide us with overwhelming evidence that in his later lectures, held around 1890,7 he regarded immanent objects as entities that have to be taken ontologically seriously. This is Brentano’s ontology of intentionality on which I want to concentrate in this section.8 What does this theory teach us ? Suppose a particular subject (John) is thinking of a particular object (let it be a highly poisonous mushroom which for some unclear reasons is placed in his refrigerator). When we are philosophically uneducated, we are tempted to think that there must be some straightforward relation between John (or John’s mind) and the mushroom in question. But the philosophers of intentionality tell us that such a picture would be far too simplified. First of all, in order to be able to think of “the highly poisonous mushroom in my refrigerator” (call it HPM for short), there need not exist any HPM at all. Imagine that John only dreamt that he collected such a mushroom in a forest and put it in his refrigerator. Or imagine that yesterday he really had it, but, unknown to him, early in the morning his wife threw it away (reasonably enough). If you want, you can even imagine that the HPM has just been annihilated by one of those deceptive Cartesian demons that some epistemologists find so fascinating. Indeed, we can create thousands of scenarios in which there is no HPM at all and in spite of this, John is still thinking “about it”. This is one of the reasons why we need a theory of intentionality. Many theories of intentionality introduce at this point an extra entity which has to replace the common-sense object of reference before the subject’s mind; and Brentano’s theory belongs to these. 4 Cf. Perler 2002, p. 228. 5 Brentano 1874/1924, p. 124. 6 Dieter Münch, Mauro Antonelli and Johannes Brandl all advocate this view. 7 This can be seen in the Logic Lectures from the late 1880’s (manuscript EL 80), in the lectures on Descriptive Psychology from 1890/91 (Brentano 1891/1982), and in the lecture On the Concept of Truth from 1889 (Brentano 1889/1930). 8 Cf. Chrudzimski 2004, Chapter 4. 2 Brentano argues that the common-sense object of reference need not exist and even in such a case, an intentional state still retains its relational character because in each intentional state, we have an immanent object before our minds. The reason why an appropriate immanent object appears before the subject’s mind every time he is thinking about something is that the immanent objects are literally “produced” by our thinking. Immanent objects are conceived by Brentano as entities that are ontologically dependent on the conscious acts in which they are thought of. But if all that is said so far is true, we now seem to be in trouble. What we wanted to explain is John’s thinking of a certain particular mushroom, but what we now get as a target object of John’s intention is some very peculiar entity that, as we just seen, is ontologically dependent on John’s mental acts. It seems to be a huge categorical mistake to think that such an entity could ever be in John’s refrigerator. But doesn’t this theory assume that John is precisely thinking this? Yes, Brentano’s theory indeed entails this strange consequence, and his answer to the above difficulty is that the immanent object before John’s mind can indeed, in a sense, be in his refrigerator. As we could imagine, the secret of this theory lies in the three words “in a sense” employed above. An immanent object, which is present in John’s thinking of the HPM, is indeed a mushroom, it is indeed highly poisonous, and it is indeed in John’s refrigerator. The immanent object before John’s mind has indeed all these properties. But the sense of being (or of having a property) expressed by the copula in the above description is a non-standard one. According to Brentano’s theory, immanent objects have all the properties that are ascribed by their subjects to the intended objects of reference, but they have these properties in a modified sense.9 Following Zalta who developed a similar theory, I will call this non-standard sense in which immanent objects have their properties encoding.10 We see that what Brentano is proposing here is a distinction between two senses of the copula to which correspond the two modes of having properties. Real horses have the property of being-a-horse “normally”, while an immanent centaur has this very same property in a modified sense. Let us represent Brentano’s theory with the following diagram: 9 Cf. Brentano 1891/1982, pp. 26/27. 10 Cf. Zalta 1988, p. 16 f. 3 Identifying property φ The immanent object has the identifying property in a modified sense The reference object has the identifying property Immanent object IMM Subject REPR Intentional Pseudo-relation Reference object The subject of the intentional state, depicted in our diagram on the left side, is thinking about the poisonous mushroom, which we find on the right side. There is between them an intentional pseudo-relation represented by a big arrow. That it does not belong to the regular extensional relations is clear from the fact that in order to obtain the intentional state, the reference object need not exist. However, within the framework of Brentano’s theory, this pseudo-relation has been replaced by another, this time fully extensional, relation. I refer here to the relation IMM obtaining between the conscious subject and the immanent object. To be in an intentional state means for Brentano to have an immanent object before one’s mind, and this “having” is symbolised in our notation as standing to the appropriate immanent entity in the relation IMM. Now, the immanent objects should, as it were, “replace” the common-sense objects of reference. They have to “represent” them for conscious subjects. The mechanism underlying 4 this representation consists in an immanent object’s having the property φ in a modified sense, which the conscious subject ascribes to his intended object of reference. We call this property the identifying property because it is the property with the help of which the reference object is “picked up” or “singled out” from the rest of the universe (of course, provided there is an appropriate object of reference at all – the condition that, as we know, need not be fulfilled). If there is an object which has the identifying property φ in the standard, non-modified sense, then we have a case of successful reference. In terms of our diagram, it means that the relation REPR obtains between the immanent object and a certain object in the world. Brentano’s theory can thus be summarised as follows: Subject S refers intentionally to object O, iff (i) there is an object x such that x stands to S in an immanence relation (x is immanent to S); (ii) x has in a non-genuine, modified sense all the properties S attributes to O; and (iii) if there is an object x which in the standard, non-modified sense has all the properties that S attributes to O, then x represents y (and, of course, in this case the object y is O). Otherwise there is no O. 2. Aristotle’s theory Is this theory Aristotelian? In order to evaluate Brentano’s self-assessment, one of course has to determine in the first place what is Aristotle’s “true” theory of Aristotle, and then compare it with the theory of immanent object outlined above. My reconstruction of Aristotle’s theory will be based on his investigations On the Soul (better known under the latinized title: De Anima). Aristotle himself did not of course speak of immanent objects in the sense outlined in the first section. Nevertheless, he formulated the theory of intentionality involving the claim that a perceived property has a non-standard mode of being within the perceived subject. A soul which is intentionally directed at something red takes, according to Aristotle, the “form” of a red thing (i.e. the redness), leaving behind its “matter”, and thus becomes – as Aristotle tells us – “in a sense” red.11 Aristotle’s medieval commentators called this kind of being “intentional”, and this way of speaking was indeed one of the sources that inspired Brentano.12 Is then the theory of immanent objects described above nothing more than the old Aristotelian idea expressed in new terms? 11 Cf. Aristotle, De Anima, 424a 11–17. 12 Cf. Brentano 1874/1924, p. 125. 5 There is indeed an important feature which the theory of immanent objects shares with the Aristotelian theory of intentionality. It consists in the introduction of a non-standard kind of exemplification. When Aristotle tells us that a soul which is intentionally directed at something red becomes “in a sense” red, then the simplest and most straightforward way of interpreting him is to assume that he is distinguishing here between two modes of exemplification and claiming that the same property of being red, which is normally exemplified by red things, will be non-standardly exemplified by any subject who is intentionally directed at something red. Also, the thesis that the mechanism of intentional reference involves the identity of properties makes this theory similar to Brentano’s views. According to Aristotle, this is the very same identifying property (in our example, the property of being red) which, on the one hand, can be possessed by the reference object and, on the other hand, is directly accessible to the subject’s mind (by being non-standardly exemplified by this very subject). In this respect, both Brentano’s theory of immanent object and Aristotle’s theory differ sharply from the representational theories, which I will discuss later. But there is also an important difference. According to Aristotle, it is not an intentional object, but a human soul which becomes “in a sense” red. This means that it is the soul which exemplifies the relevant property in a non-standard sense. And, since the soul is according to Aristotle the very form of a human being (i.e. that aspect of a conscious subject which makes it into what it is), one can say after all that this is a conscious subject considered as a whole, which exemplifies the relevant property in the non-standard sense. Let us call this mode of exemplification “exemplification*”. Accordingly, the Aristotelian picture of the intentional reference would look like this: 6 Identifying property: Aristotelian form ϕ The subject (soul) has the identifying property in a modified sense Subject The reference object has the identifying property Intentional pseudo-relation Reference object The similarities between Aristotle and Brentano can be summarised as follows: (i) Both introduce entities which mediate the intentional reference. (ii) Both assume that this is the very same property that, on the one hand, stands before the subject’s mind and, on the other hand, can be exemplified by the reference object. (iii) Both introduce a certain non-standard mode of exemplifying properties. And here are the differences: (i) mediating entities Brentano Aristotle immanent objects ‘bare’ properties (ii) cognitive accessibility of only as encoded by immanent ontologically directly by the identifying properties objects via relation IMM exemplification* (iii) non-standard encoding exemplification* exemplification Needless to say, interpreting Aristotle is an extremely challenging task. What I have said here is just a first approximation and I do not claim that this construal is the only possible one. In particular, it is possible to claim that the Aristotelian being “in a sense” should be interpreted 7 in terms of intentional objects (this was, as it seems, the interpretation of Brentano in his Psychology)13 or that having “in a sense” the property φ amounts, in the end, to having (in the normal standard sense) another property (say,ψ), as some scholastics seem to interpret him.14 According to the first interpretation, Aristotle’s theory would simply be a disguised expression of a theory of immanent objects. According to the second, it would amount to the theory of mental representation which we shall soon analyse. I believe that what Aristotle actually said justifies neither of these interpretations. What he has said suggests the picture which I have sketched above with the non-standard exemplification of a property by a human soul as an ontologically primitive notion. In comparison with the theory of immanent objects, Aristotle’s theory introduces a similar complication in the most primitive metaphysical concepts (a primitive non-standard kind of exemplification), but structurally it looks much simpler, as it involves neither the category of immanent objects nor the relation IMM. Ontological simplicity is of course a prima facie advantage, but there seems to be real benefits to introducing immanent objects as “bearers” of identifying properties. Consider the following problem. Within the framework of our theory of intentionality, we want to be able to distinguish between two situations: (i) a simultaneous thinking of two different things: a red thing and a triangular thing; (ii) a thinking of something which is both red and triangular. The theory of immanent objects provides a straightforward answer to the question as to where the relevant difference lies. In the case of (i), we have before our mind two immanent objects, each of which encodes only one of the aforementioned properties. In the case of (ii), we have only one immanent object, encoding both redness and triangularity. Aristotle puts forth no answer to this problem. At first sight, it seems that in both cases the Aristotelian subject must exemplify* both redness and triangularity.15 This is why I prefer the theory of immanent objects. But regardless of our sympathy or antipathy toward the Brentanian or Aristotelian approach, we see that we have here two quite different ontologies of intentionality. 13 Cf. Brentano 1874/1924, p. 125. 14 Cf. Perler 2002, p. 70 f. 15 There are of course various ways of reconstructing this difference within the Aristotelian framework, but they would all deprive the Aristotelian picture of it initial attractive simplicity. E.g. we can introduce compound properties and differentiate between “a’s exemplifying* [F+G]” and “a’s exemplifying* [F] and a’s exemplifying* [G]”, or we can introduce “plural modes” of exemplification* and similarly distinguish between “exemplifying* (jointly) (F and G)” and “exemplifying* F and exemplifying* G”. 8 3. The theory of ens objectivum An analysis of the phenomenon of intentionality which seems closer to the theory of immanent objects is the medieval theory of the ens obiectivum, developed mainly by Duns Scott and his school. This theory states that in all cases of intentional reference, the object which is intentionally referred to is provided with an “objective” being “within the subject’s mind”. The object is thus “objectively” in the subject’s mind, regardless of whether or not it also has “real” being in the extra-mental world. The metaphor of “being in the mind” refers here not only to the object’s cognitive accessibility, but also to its ontological dependence on the thinking subject. The object in question has the objective mode of being only insofar as it is thought of. What distinguishes the theory of the ens obiectivum from the Aristotelian picture is the fact that one speaks here of the objective existence of the object of reference, and not of a non-standard mode of having the identifying property. What is objectively in the subject’s mind is thus a red apple, not the redness and the applehood. Structurally, this theory is indeed much more similar to the theory of immanent objects outlined above, but we do also find here some crucial differences. First of all, the theory of the ens obiectivum says nothing about any non-standard sense in which entia obiectiva should have their properties. It may sound strange, but an apple, which is objectively in a subject’s mind, is supposed to be an apple in the absolutely standard sense of the word “is”. What saves this theory from an overt absurdity is the thesis that the objective mode of being which an apple enjoys within the subject’s mind involves no ontological commitment. The expression entia obiectiva, was introduced merely to serve as a convenient façon de parler, which did not expand our ontology.16 Brentano’s theory of immanent objects, outlined in the first section, does not claim this. It regards intentional objects as a full-fledged ontological category. Their mode of being is by no means “weaker” than the mode of being that is characteristic of tables and cats; and this was precisely the reason why it was necessary to introduce a non-standard mode of exemplification. The similarities between the theory of immanent objects and the theory of ens obiectivum thus consist in the fact that: (i) both theories introduce mediating entities that have 16 This ontological neutrality was a characteristic of Duns Scott’s theory. However, some of his followers saw this rather as a disadvantage. Cf. Perler 2002, p. 228. 9 an identifying property, and (ii) both treat these mediating entities as ontologically dependent upon the conscious subjects that use them. The differences between them may be summarised as follows: immanent objects ens obiectivum encoding standard exemplification (ii) what is the kind of being standard, ontologically ontologically non-committing characteristic of mediating committing being “objective” being (i) how mediating entities have their identifying properties entities The picture of intentionality proposed by the proponents of entia obiectiva looks like this: Identifying Property Ens obiectivum has the identifying property in the standard sense This “cloud” contains all that is “in subject’s mind” (and that has eo ipso an ontologically noncommitting mode of being) ϕ The reference object has the identifying property ens obiectivum IMM Subject REPR Intentional pseudo-relation Reference object 10 The two characteristic features of the ens obiectivum theory are: (i) the fact that the mediating entities have their properties in the normal sense, and (ii) the fact that their mode of being is quite different from the mode of being characteristic of the citizens of the real world. Both features make this theory similar to the theory of intentionality developed by Alexius Meinong. According to Meinong, a subject who imagines a Golden Mountain must have before his mind an entity which has the property of being a Golden Mountain. Furthermore, this entity has the relevant property in the absolutely standard sense. Meinong’s copula is not ambiguous.17 In these two respects, Meinong’s theory is thus like the theory of the ens obiectivum. There is also another aspect which makes them similar. To avoid postulating a real Golden Mountain, Meinong introduces objects that have a very special ontological status. In a(n) (in)famous remark, he says that the objects, which in every intentional state stand before a subject’s inner eye, are “beyond being and non-being”.18 How to interpret this kind of being is a very difficult question,19 but the most interesting way is probably to construe it as an ontologically non-committing one.20 But there is also an important difference between Meinong and proponents of the theory of objective mode of being. While the supporters of the ens obiectivum theory construe their ontologically neutral, objective existence as a subject-dependent kind of being (as a being “in the subject’s mind”), Meinong’s objects, which are “beyond being and non-being”, are conceived as radically mind-independent. If there were no conscious subjects, there would be, according to the Scottists, no entia obiectiva either. In contrast, according to Meinong, the world would still be populated in this case by strange entities that are “beyond being and nonbeing”. As mentioned before, the model of intentionality employed by the young Brentano resembles the theory of ens obiectivum much more than the ontologically full-blown theory of immanent objects. It is also very characteristic of the late Brentano who rejected all entities that did not belong to the category of things that he tried to persuade his students that he never 17 On this topic, cf. Reicher 2001. 18 Cf. Meinong 1904. 19 Cf. Chrudzimski 2005. 20 On such an interpretation cf. e.g. Routley 1980. 11 held the theory of immanent objects of the type outlined in section 1.21 True enough, there is indeed overwhelming textual evidence that Brentano developed in his lectures something along the lines of what is put forward in section 1, but it is equally true that the corresponding developments were never published by him. It is therefore not excluded that the ontologically articulated theory of section 1 figured in Brentano’s thought only as a kind of hypothesis that he tested during his lectures, but never fully accepted and finally explicitly rejected. So it is not excluded that the theory of ens obiectivum sketched in the present section must be regarded as Brentano’s “official” doctrine until 1904. 4. The representational theory sensu stricto As indicated, Brentano had a tendency to interpret the Aristotelian theory of intentionality in the vein of Scholasticism. But it is by no means clear that the ens obiectivum construal always prevailed, and this fact further complicates the question of Brentano’s own assessment as an Aristotelian. In his Habilitationsschrift, which was explicitly devoted to Aristotle’s philosophy of mind, we find an interesting analysis that suggests another interpretation. It begins with a summary of the doctrine of the ens obiectivum as applied to Aristotle. Brentano says explicitly that, following the schoolmen, he uses the notion of objective existence as a tool22; and he attributes to Aristotle the view that the perceived object has an objective mode of being within the perceiver’s mind. But after this claim, he says something strange, something that changes the whole picture. Every time a conscious subject perceives an object A, we read, it is not A itself, but rather “an analogue” of A which is in the subject’s mind. This “analogue” (call it A*) only represents the genuine objects of reference for the subject. What is the mechanism underlying this representation? A* has some properties which vary in a systematically dependant way upon the changes in the properties of A and only in this way can the subject (who has A* and not A within his mind) know something about the changes in A.23 21 Cf. e.g. the widely cited letter to Kraus: “Es ist aber nicht meine Meinung gewesen, daß das immanente Objekt = ‘vorgestelltes Objekt’ sei. Die Vorstellung hat nicht ‘vorgestelltes Ding’, sondern ‘das Ding’, also z.B. die Vorstellung eines Pferdes, nicht ‘vorgestelltes Pferd’, sondern ‘Pferd’ zum (immanenten d.h. allein eigentlich Objekt zu nennenden) Objekt. Dieses Objekt ist aber nicht. Der Vorstellende hat etwas zum Objekt, ohne daß es deshalb ist.”, Brentano 1977, p. 119 f. 22 Cf. Brentano 1867, p. 80. 23 Cf. Brentano 1867, p. 94. Brentano doesn’t use the word “representation”. 12 What we find here is definitely neither (1) the ontologically substantial theory of immanent objects, nor (2) Aristotle’s theory as sketched above in section 2. But it also does not resemble (3) the theory of the ens obiectivum. Brentano speaks here neither of any special mode of exemplification, which excludes theories (1) and (2), nor of any special mode of being, which excludes (3). What we get instead is a theory of representing entities, (i) whose mode of existence is ontologically-committing and (ii) which have their representing properties in the standard, non-modified sense of the copula. These two aspects already distinguish this theory from all the theories that we have seen so far. But there is still another, much more important, aspect in which it differs from the others. According to the current position and in opposition to all the theories analysed above, (iii) the representing properties of the postulated entity are different from the identifying properties of the genuine object of reference. In this sense, the theory of mental representation in Brentano’s Habilitationsschrift can be termed a representational theory, while the three theories analysed earlier can be called presentational ones (as they assume the identity of the representing and the identifying properties). But as the word “representational” is nowadays used in a very broad sense, I will call the present theory the representational theory sensu stricto. It may be illustrated by the following diagram: 13 Identifying property Representing property ϕ ψ REPR* Representing entity has the representing property in the standard sense The reference object has the identifying property Representing entity IMM Subject REPR Intentional pseudo-relation Reference object Of course, we find here some similarities to the earlier theories. The subject is directed at the reference object by means of standing in a certain relation to a certain postulated entity. We still call this relation IMM. If there is an appropriate object of reference in the world, then the representing entity stands in relation to this object by way of REPR. But there is also a big difference. The representational theory sensu stricto introduces two kinds of properties (representing and identifying ones) and stipulates a peculiar “connecting” relation between them (REPR*). This connecting relation becomes one of the central elements of this picture of intentionality. In the “presentational” theories, the identifying property φ has been directly “put before the subject’s mind” (either as an encoded property of the intentional object, or as an exemplified property of the ens obiectivum, or as a “bare” property exemplified* by the subject’s soul), but in the representational theory sensu stricto the identifying property φ is accessible only via the representing property ψ and the connecting relation REPR*. 14 5. Conclusion We may now try to answer the question as to why Brentano classified his theory as Aristotelian in spite of the formidable structural differences between his theory of immanent objects and the Aristotelian approach as outlined in sections 1 and 2. It seems that he did so basically for two reasons. First of all, he had a tendency to regard the entire spectrum of medieval theories of intentionality reaching from the Scottist theory of the ens objectivum to the theory of inner language of William of Ockham as varieties of the Aristotelian view.24 True enough, one could hardly find a single medieval philosopher who would not consider himself a true Aristotelian (and quite often even as the only true Aristotelian), but we know very well today that to see all these subtly distinct theories as species of one homogeneous Aristotelian genus would amount to an obvious oversimplification. Nonetheless, Brentano seemed to see things this way and since his early theory was very similar to the theory of the ens objectivum, he automatically interpreted it as Aristotelian. Moreover, we have seen in section 4 that he sometimes interpreted the theory of the ens objectivum (and a fortiori Aristotle’s theory as he saw it) as a species of the representational theory sensu stricto! This is almost certainly a huge mistake, but Brentano really made it in his Habilitationsschrift. The first reason why Brentano could claim that his theory of intentionality was Aristotelian in nature thus lies, roughly speaking, in the vagueness of his picture of Aristotle’s theory. The second reason is more interesting. Even while operating within the framework of his mature theory of immanent objects, as sketched in section 1, Brentano believed himself to be able to find an Aristotelian counterpart to the idea of having properties in a non-standard mode, which as we have seen, is absolutely central to his ontology of immanent objects; and he was certainly right. This is of course the Aristotelian non-standard exemplification. As we have seen, within the framework of Aristotle’s theory we do find another non-standard exemplification other than that of encoding, which is characteristic of the Brentanian account of immanent objects, but the idea of distinguishing various copulas was indeed one of those isolated (but nonetheless very important) elements that Brentano took from his master. 24 Cf. e.g. Brentano 1874/1924, p. 124 f., where he lumps together Aristotle, Neo-platonists, and many schoolmen. 15 References Binder, Thomas/Fabian, Reinhard/Höfer, Ulf/Valent, Juta (eds.), (2001) Bausteine zu einer Geschichte der Philosophie an der Universität Graz, Amsterdam/New York: Rodopi. Brentano, Franz, (1862) Von der mannigfachen Bedeutung des Seienden nach Aristoteles, Freiburg i. Br.: Herder [Dissertation]; unveränderter Nachdruck: Hildesheim/Zürich/New York: Georg Olms Verlag 1984. 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