Like only few contemporary philosophers, Peter Rohs has covered the entire traditional domain of philosophy in his extensive body of work, which has been growing over the past five decades. Indeed, there is no central area of philosophy, from philosophy of science to ethics, from the philosophy of language to natural philosophy, to which Rohs has not made important, standalone contributions. The historical reference points of his thinking include—beside Plato, Aristotle, Neoplatonism, Spinoza, Fichte, and Hegel—Frege and, most importantly and time and again, Kant. After making a name for himself by means of his still relevant dissertation on Hegel’s science of logic, Peter Rohs became known in the 1970s above all as a creative interpreter of Kant. From the very beginning his interest in Kant, however, was not primarily historical but philosophical. Already in his first book on Kant, the Transcendental Aesthetic (1973), he developed, at the time still explicitly working from Heidegger, the basic systematic idea that became the focus of his thinking, about which he has since written six monographs and numerous essays. Rohs’ basic idea has to do with the connection between time and subjectivity. This connection is also the focus of this new book by Peter Rohs, in which he gives an overview of his philosophy, and—in light of his last comprehensive work Feld-Zeit-Ich (1996)—revises and develops its important points.
Things in Themselves and Appearances
In his new book, Peter Rohs develops his analytic transcendental philosophy, which is how he now refers to his position, as a transformation of the Kantian dualism of appearances and things in themselves. In place of the latter, Rohs posits the four-dimensional spacetime field whose temporal dimension only includes the static relations of being earlier, later, and simultaneous, which Rohs thus refers to as “block universe.” Belonging to this universe are all material objects and physical processes. The domain of the mental, on the one hand, and senses, concepts, meanings, and facts, on the other, are not part of the physical universe. Rohs understands facts along with Frege as true propositions, which are the contents of our propositional attitudes of believing, wishing, etc. According to Rohs, mental processes and their propositional contents (and their components) cannot be adequately described and explained in a purely physical vocabulary. They are based on the spontaneous activity of the subject, which presupposes the distinction of past, present, and future, which does not exist in the “block universe.” The result is a fundamental dualism of a physically describable reality on the one hand and the mental (including propositions and facts) on the other, according to which the physical reality corresponds to the Kantian things in themselves and the mental has the status of an appearance. In this way the Kantian distinction undergoes an important transformation. The Rohsian things in themselves are, unlike for Kant, not uncognizable but (akin to Sellars) the objects of natural scientific knowledge. And Rohsian appearances are not appearances of something intelligible or supersensible, but “appearances” only insofar as they are, first, no part of the physically describable reality “in itself” and, second, depend on subjective activities.
This transformed dualism of things in themselves and appearances underlies the dualism between (what McTaggart called) A- and B-determinations of time. What does this mean?
Working from McTaggart and Heidegger, Rohs distinguishes between two fundamental, non-reducible aspects of time. On the one side are time determinations that are expressible using temporal relations like “earlier than” or “simultaneous with.” These are the so-called B-relations. They allow us to order events temporally, since for each pair of events E1 and E2 it holds that E1 occurs either earlier or later or simultaneously with E2. That an event occurs earlier, later, or simultaneous with another is itself, however, not an event that occurs earlier or later than other events: the question when is E1 earlier than E2 does not make sense. If lightning is earlier than thunder, one can ask when exactly did the lightning occur, and when the thunder, but one cannot meaningfully ask when the lightning was earlier than the thunder. When the lightning struck? Or when it thundered? These questions are not meaningful.
B-relations hence characterize an oddly static aspect of time. This becomes especially clear if we view, like contemporary physics, temporal B-relations as part of four-dimensional spacetime, which Rohs refers to as “field” or “block universe.” Next to the three spatial dimensions, physical reality is characterized by an “earlier” and “later” temporal dimension. Each concrete event is then representable as a point or set of points in a four-dimensional coordinate system, where each point is uniquely determined by three space coordinates and a time coordinate. A national football game, for instance, is uniquely characterized by its occurring on this or that day from 3:30 p.m. to 5:15 p.m. in this or that stadium. The static aspect of this image of reality becomes apparent in that all points in time are equally real: just as points in space farther away from the origin of the coordinate system are no less real than those in the proximity of the origin, so are later points in time no less real than earlier ones and vice versa. While it is of course correct to say that the kick-off occurs earlier than the final whistle, this does not mean that the final whistle is a lesser component of the football game than the kick-off. What is missing from this picture of reality is the dynamic aspect of time, which is what makes a football game exciting in the first place: the final whistle (and with it the entire game) lies in the future at the point in time of the kick-off.
At first glance it could seem as if this simply means that the final whistle is later than the kick-off. But this is not the case. That the final whistle is later than the kick-off itself does not occur at a point in time; it does not make sense to ask when it is later than the kick-off. By contrast, one can absolutely ask when the whistle lies in the future—namely until it is present. This differentiation of past, present, and future cannot be depicted in a static, four-dimensional coordinate system, since with each moment another point in time is present. Relative to this point in time, all earlier points in time are in the past, all later ones in the future. To be future, present, and then past can be called, with McTaggart, A-determinations of time; their change—that an event is initially in the future, then present, and finally in the past forever—is what is called, somewhat misleadingly, the “flow of time.” Rohs speaks instead, following Bieri, of “temporal becoming.” For good reasons, which I cannot present in detail here, Rohs holds that A- and B-determinations of time are not reducible to each other (cf. Chapter 2 of this book): both are equally fundamental for the total phenomenon of time. With Rohs’ earlier formulation, we can thus speak of a “temporal dualism.”
It is noteworthy that a scientific image of the world seems to manage with B-determinations alone. Put differently, in scientific theories, especially in physics, there is no place for A-determinations. While many physical, chemical, and biological phenomena have a unique temporal direction, since there are irreversible processes, their explanation is possible without appealing to A-determinations. The reality of A-determinations is thus often disputed by physicists (and physicalist philosophers).
The Philosophical Relevance of Temporal Dualism
Up until now we have dealt with a purely time-philosophical distinction, the relevance of which might be thought to be very limited. But in fact numerous other philosophically important dualisms can be traced back to this internal dualism of time, according to Rohs, such as those of body and mind, subjectivity and objectivity, abstract and concrete, general and particular, psychical representations and truth-apt propositions, natural causality and freedom, explaining and understanding, things and facts, and things in themselves and appearances. According to Rohs, all these seemingly unrelated distinctions deal with the difference between, on the one hand, things whose temporal structures are given by B-determinations alone, and, on the other hand, things whose understanding in addition requires recourse to temporal becoming and A-determinations. It would be beyond the scope of this introduction to develop this idea in full. Instead I will have to limit my presentation to introducing the particular traits of temporal becoming that make it, according to Rohs, into a philosophically central phenomenon and discuss them (in part independently of Rohs’ own considerations). In conclusion, I will look at a thesis that is fundamental to Rohs’ philosophy, namely that temporal becoming is constitutive for subjectivity.
Temporal becoming has, according to Rohs, a number of traits that become especially relevant for the explanation of subjectivity: First, it is a process sui generis, which is fundamentally different from natural processes in time; second, we do not perceive this process with one or more of our senses; it is thus a non-sensible process; third, it is nevertheless something real that undoubtably belongs to reality; and fourth, temporal becoming is something objective or at least intersubjective, since the present is the same for all subjects. I would now like to discuss each of these points in turn to see what they mean for the relation between temporal becoming and subjectivity.
Temporal Becoming as a Non-natural Process
Temporal becoming is, according to Rohs, a process sui generis, which is principally different from natural processes in time. Consider a simple physical process such as the sun warming a stone. The stone is initially cold, later it is warm. The change hence consists in something different being the case at two different points in time. This is an intra-temporal process, that is, a process in time. Temporal becoming, by contrast, consists in something different being the case at the same point in time: The point in time at which the stone is warm is first in the future, then it is present, and finally in the past. Here, nothing changes in the temperature of the stone or in its other properties; the only thing that changes is the temporal position relative to the present, which is a change completely different from intra-temporal changes in an object’s properties and relations. As mentioned before, intra-temporal processes have a speed while temporal becoming does not. The stone can become warm within a minute or within an hour, but an hour cannot pass quickly or slowly. Of course, time can seem long to me, until the hour has passed, whereas in other situations time flies. But this concerns a purely subjective phenomenon, just as the same path can appear long at times and short at others. Of course, it is always the same length of time until an hour is over, namely sixty minutes. What could it then mean to say that the hour passes slowly or quickly? Perhaps this: the present wanders along the minutes of the hour or along the events occurring in this hour sometimes faster and sometimes slower. But this does not make sense: we would then need a “second time” with second-order points in time, with respect to which we could ask how long an hour lasts (without the answer being, trivially, sixty minutes). Since there is no such “second time,” temporal becoming has no speed. It is indeed an entirely peculiar process escaping physical description, since physical processes always have a speed, are datable, and assume a place in time.
Temporal Becoming as a Non-sensible Process
Second, according to Rohs, temporal becoming is a non-sensible process, that is, it is a process that we cannot perceive because it does not affect our senses. It is not immediately clear whether this thesis is justified. That the known forms of sensible perception like seeing, hearing, and smelling require a causal affection of our sense organs by the perceived object should be uncontroversial. What is disputable is that this is a conceptual truth. There are philosophers who take it to be at least conceivable that there is perception even without a causal contact. According to these philosophers, it is an empirical fact that there are clairvoyants, but it is no conceptual or necessary truth. It would be accordingly at least conceivable that we perceive temporal becoming even if it exerts no causal influence on us.
But even if perception should necessarily involve a causal relation, the further question remains whether temporal becoming might not affect one of our senses after all. That we do not possess a sense organ that perceives time does not rule out a specific temporal perception, since other senses, like proprioception (the direct perception of the relative position of one’s body parts), are not based on the affection of a sense organ.
A convincing argument against a sense affection through temporal becoming would result if we were allowed to assume that only things and events that can be located within space and time (Rohs’ block universe) could enter causal relations; since temporal becoming, as we have seen, is no datable event, it would then be impossible for it to affect our senses. However, Rohs himself grants that there is, in addition to physically describable causal relations between datable events, another form of causality, namely causality from freedom, so that this argument is not open to him. Why should the perception of temporal becoming not be likewise based on a specific form of causality?
Perhaps a weaker version of the causality thesis might be sufficient: Not every causal relation but every affection of a sense organ must occur in a causal succession of datable events; if this were not the case, sensible perception would not be a natural process. But this argument is also not convincing, since if temporal becoming is indeed a non-natural process sui generis, one can also not expect the perception of it to be a purely natural process.
I thus come to the conclusion that, contrary to Rohs, it cannot be ruled out that our knowledge of the passing of time is based on sensible perception. This does not undermine Rohs’ main point, however, if it is reformulated as follows: our epistemic access to temporal becoming is fundamentally different from our access to natural, internal temporal processes. If temporal becoming should be perceivable by the senses, then it is so in a fundamentally different way than natural processes, namely without affecting us causally or by affecting us and in a way that is not natural causality. Whether one wants to refer to such processes as sensible perception, non-sensible perception, or as something other than perception, appears to be merely a terminological question.
Temporal Becoming as Part of Reality
I now arrive at the third point, which concerns how temporal becoming is a real phenomenon despite its physical irreality. It could appear as if Rohs has changed his position on this point, since he now emphasizes, in opposition to earlier works, that temporal becoming is not “real” and the phenomena based on it are mere appearances. But this is only a shift of terminology. Temporal becoming, or the present, is actually only unreal to the extent that it is no part of physically describable reality; and the mental (as well as the world of senses, meanings, and facts) is only an appearance to the extent that it depends on subjective capabilities—on the spontaneous “activities” of the subject. But this does not mean that these are not irreducible aspects of reality that exist in a metaphysically robust sense.
The difference between past, present, and future is indeed so central to our self-understanding and understanding of the world that its irreality is hard to imagine. But is its existence evident and indisputable? It was after all Albert Einstein who, as Rohs mentions, held it to be a stubborn illusion. Is the Euclidean character of space not just as evident as the flow of time, yet still an illusion? One could respond that in the mesocosmic domain of human experience the difference between Euclidean and non-Euclidean space are insignificant, whereas the distinction between the static time of physics and temporal becoming is central to our entire life. In particular, human action is based on the difference between a closed past that can no longer be influenced and an open and malleable future, separated by the present as the point in time in which we must act. In his more recent works, Rohs expresses this thought in a Heideggerian way by saying that the future is “what we care about” (“dem unsere Sorge gilt”). For acting beings, temporal becoming is thus indeed evident and indisputable.
One could perhaps attempt to use the relation between action and temporal becoming as the basis for a transcendental argument: whoever acts presupposes the reality of temporal becoming; the skeptic of temporal becoming also acts, as denying a thesis is an action; therefore, the skeptic must acknowledge the reality of temporal becoming. But such an argument does not appear to me to be very promising. Someone who delegates all questions about what exists to the natural sciences will not be impressed by the argument; all they must do is accept that human action is an illusion, too. At least from a purely theoretical perspective the resulting view seems to be consistent.
What then is the argumentative role, if not that of a premise in a transcendental argument, of Rohs’ claim that there can be no action without temporal becoming? I would like to suggest understanding it as part of an argument-form that Hilary Putnam has called “indispensability arguments.” In contrast to transcendental arguments, the aim of arguments of this form is not to entangle a skeptic—in our case the skeptic of the reality of temporal becoming—in a contradiction but to indicate that the doubted thesis is indispensable for a certain well-established praxis. For instance, Quine argued for the reality of sets as abstract objects by pointing to their indispensability for mathematics and the natural sciences. There could obviously be radical nominalists who would be prepared to deny the truth both of mathematical and scientific statements. They could thus avoid Quine’s argument. The charm of this argument, however, is that no reasonable person will seriously doubt his or her pay stub or the statics of a bridge because of skeptical concerns about sets and abstract objects. It would be just as absurd, in my opinion, to doubt the reality of human action only because temporal becoming is not posited by (current) physical theories. The converse approach is instead reasonable: to accept the reality of temporal becoming because it is indispensable for human action. This pragmatic argument-form, less ambitious than transcendental arguments but equally effective, fits Rohs’ holistic conception of philosophical justification, which doesn’t search for ineluctable fixed points but calls for a reasonable weighing of reasons and counter-reasons.
The only reason speaking against the reality of temporal becoming is that it does not exist in physics. In light of its indispensability for human action, this reason is not sufficient to deny its reality. Pace Einstein, temporal becoming is no illusion but an irreducible aspect of reality (which transcends what is describable and explainable by current physical theories).
Temporal Becoming as an Intersubjective Phenomenon
I now arrive at the fourth point, which concerns how temporal becoming is not a physical process, nothing private, but something intersubjective. Rohs speaks of the “specific intersubjectivity of the subjective,” which, according to him, is already at the basis of the Kantian a priori.
That temporal becoming is intersubjective means that there is only one present that is the same for all subjects. The same point in time that is present for me right now is also present for all other subjects. This raises the question whether the present is punctiform or has a temporal extension. Psychology teaches the latter: The length of an experienced period of time as present is measurable if one presents various stimuli in very short intervals and asks test persons whether they perceive them at the same time or not. These experiments show that the experienced present is not punctiform but comprises a time interval in magnitude of several milliseconds; everything within this interval is experienced as present even if it is not strictly simultaneous. In this sense, it is possible that the present of various subjects is not completely synchronous, since the intervals experienced as present could be different lengths. Rohs’ thesis of the intersubjectivity of temporal becoming does not have to contradict this as long as the time intervals experienced as present by different people always overlap. At the intersection of these intervals lies, then, the present point in time. But whereas the length of the experienced present can be empirically investigated, the question whether the intervals experienced as present by two subjects overlap or not is empirically undecidable. For there to be an empirical answer to this question, one would have to obtain an informative answer to the question which point in time is present right now for a certain subject. But the only possible answer is: “The present point in time.”
It is a very unsettling thought that different subjects could experience different points in time as present. Whereas the present moment for one person attending an opera performance is when he hears the overture, the opera is perhaps already over for his neighbor! Nothing in the physical description of a visit to the opera rules out such an asynchronicity of presents, since the distinction between past, present, and future does not appear at all, as mentioned, in that physical description. Such a scenario, like other skeptical scenarios, can hardly be ruled out empirically. There is in any case no empirical evidence that could refute it.
We must ask, however, whether the scenario of asynchronous presents is really consistent. I think that upon closer consideration we can see that this is not the case. If we conceive of physically describable reality as a four-dimensional spacetime field, then two simultaneously living humans A and B exist in two different spacetime areas that overlap in the temporal dimension. Let us now assume that A experiences as present point in time t1. Would it be conceivable for B to experience a later point in time t2 as present? Asked in this way, the answer is: Yes, B can experience a later point in time t2 as present if this happens at a time different from (later than) the one at which A experiences as present t1. This leads trivially to t2 being experienced as present later than t1, but there is obviously no asynchronicity of the presents of A and B involved in this possibility. For the possibility of an asynchronous present, one would have to add that t1 for A is present at the very same time t2 is present for B. But this addition does not make sense. If the hypothesis of the asynchronous present is to be meaningful, one would have to be able to ask, for instance, when (at which point in time) the overture is present for A and the final cord present for B. The answer could not be “at the time of the overture,” since it would be wrong to say that for B the final cord is present at the time of the overture. For the same reason, the answer cannot be “at the time of the final cord,” since then for A the overture would have to be present at the time of the final cord, which is likewise not true. That for A the overture and for B the final cord could be present at a third point in time, whether earlier or later, is obviously false, too. This means that the point in time at which for A the overture and for B the final cord is present cannot belong to the same series of points in time as those of the overture and the final cord. What one would need in order to make understandable the hypothesis of the asynchronous present would be second-order points in time, or points in a time in which points in time could occur, but these do not exist. The worry that my own and my neighbor’s present might not be synchronous thus proves to be ungrounded.
Temporal Becoming and Subjectivity
Thus far, we have discussed the four traits of temporal becoming: its non-natural character, its non-sensibility, its reality, and its intersubjectivity. I now arrive at Rohs’ basic insight, which is that subjectivity is based on temporal becoming and can be explained by appeal to it. Specifically, what is at issue is one modality of temporal becoming, namely, presence (being present). The main idea, which Rohs refers to as the “specific constitution thesis,” is that presence (and thus the difference of past, present, and future) is constitutive for subjectivity and the mental. Conversely, the way in which we become conscious of our own mental state is constitutive of something’s being temporally present. This is referred to by Rohs as the “ideality thesis.” He thus revises his earlier view of temporal becoming as being mind-independent. His new view entails that points in time of the remote past that no thinking being experienced were never present.
According to Rohs’ current position, temporal becoming is just as dependent on our mind as the mind is on temporal becoming. I would like to conclude by taking a brief look at one direction of this dependence, namely, the dependence of the mental on temporal becoming.1
The thesis that temporal becoming is constitutive for the mental is supported by a number of points that are striking, even though they are not properly taken into consideration by contemporary philosophy of mind. I will list only four of these points: First, temporal becoming and the specifically subjective character of the mental, which is only revealed in the first-person perspective, seem to escape a description and explanation in terms of physics (and natural science). If this is true, then both drop out of reality as described by the natural sciences. Second, we can only access our own mental phenomena in the mode of the present. That is, we can recall past joys and fear future pain, but we can only be immediately conscious of these memories and fears, as well as current experiences, in the present. If self-consciousness is knowledge of our own mental states, then self-consciousness is always also consciousness of what is temporally present. The same dependence on the present is also shown on the level of mental states themselves. Thus, third, perception—our access to the empirical world—is always perception of the present. We can recall past events and anticipate future ones, but we can directly perceive only present events and things. And, fourth, our will is always based on the present and directed to the future; we act now for the future because we “care,” as Rohs says in allusion to Heidegger.
These points indeed make it very plausible that temporal becoming is constitutive for our minds: there are no mental processes, consciousness, or subjectivity without temporal becoming.
To understand the relevance of this thesis, it is helpful to clarify the difference between mental and non-mental events. For both kinds of events it is true that present events are “real” in a specific sense and that nothing can be real in this sense that is not present. This means that temporal becoming brings with it a characteristic difference in the reality of events: Whereas future events are not yet real and past events are no longer real, only present events are real in this specific present-tensed sense. Future events are in this sense not real at all, past ones are real, at least derivatively, since they were at least present at one time. In a non-present-tensed sense, by contrast, an event is real if (and only if) it is a part of the physically describable spacetime reality, in which—as mentioned—the distinction between past, present, and future doesn’t occur. Spacetime events can thus be real in a present-tensed sense as well as in a non-present-tensed one, but mental events can be real only in a present-tensed sense. This does not rule out mental processes having a material substrate, but it means that such a substrate alone cannot explain the specific subjectivity of the mental.
Rohs thus provides an answer to the fundamental question of the philosophy of mind, namely, the question concerning the ontological status of the mental. The mental, as Rohs put it with Kant, is an “appearance,” ontologically dependent of our mental access to it, the access of which is always linked to the “form of intuition” of temporal becoming, thus occurring in the mode of the present. Since material reality as such does not underlie temporal becoming, the ontological difference between body and mind, according to Rohs, is grounded in their different temporal properties. The constitutive role of temporal becoming for the mental therefore opens up an important perspective for the philosophy of mind, which Rohs discusses in detail in this book. In this way, the non-natural and non-sensible character of temporal becoming, according to Rohs, ensures the immateriality of the mental, whereas the pragmatically indisputable reality of temporal becoming protects the mental from any attempt at its theoretical elimination. At the same time, the specific intersubjectivity of the present is a starting point for explaining the communicability of the contents of our mental states. It thus becomes obvious that the connection between time and subjectivity is of great importance to the philosophy of mind.
As Rohs has argued in numerous earlier works, and as this book shows again, the distinction between A- and B-determinations of time makes it possible to develop solutions for a number of important philosophical problems beyond the philosophy of mind: the problem of universals, the question concerning the status of meanings and propositions, the possibility of linguistic communication, the question concerning the freedom of the will, and, last but not least, the problem of mind-body interaction. More can be found on these themes in the following chapters. In this introduction, my intention was only to elaborate an aspect of Rohs’ thinking that I take to be fundamental, namely, the hardly disputable but widely ignored link between temporal becoming and subjectivity. Making us aware of its central relevance, and pointing out its consequences, is one of the greatest philosophical achievements of Peter Rohs.
This introduction is based on a text that was published in Information Philosophie in 2006; it has been supplemented and revised to a great extent in view of the present book by Peter Rohs.