Capstone: Kantian Time and Einsteinian Relativity

In this essay, I will argue that the Kantian time presented as an a priori form of intuition is not compromised, but rather strengthened by Einstein’s theory of relativity. First, I’ll contextualize Kant’s writing in the Critique of Pure Reason with Newtonian absolute time. Here, I’ll mainly reference Robert DiSalle’s Understanding Space-Time to explain Newtonian absolutism. Then, I’ll explicate in detail the Kantian form of time as outlined in the Transcendental Aesthetic section of the Critique. Next, I’ll describe Einsteinian relativity and its associated observer-dependance. Following this, I will meditate on the interplay between relativity and the Kantian form of time, suggesting that relativity is an empirical development that both presupposes and reinforces the Kantian transcendental temporal ideality. In this last section I will reference both Thomas Ryckman’s The Reign of Relativity: Philosophy in Physics 1915-1925 and Michael Friedman’s Kant and the Exact Sciences, in part to provide needed context from the philosophy of science.

The temporal ideas of Newtonian absolutism predate Kant’s temporal transcendental idealism presented in the Critique. Newton supposed, regarding time, that it inherently maintained an absolute character: “‘Absolute time, without reference to anything external, flows uniformly’” (DiSalle 20). To Newton, time (and space) could and did exist completely independently of relations of objects or to any observer with a certain objective independence as a distinct entity. Contained within the Newtonian definition of time are the following: the “absolute equality of time intervals (‘uniform flow’), and, less obviously but equally essentially, absolute simultaneity” (DiSalle 20). Simultaneity would provide ordering of events across space in time, and equality of time intervals grounded the consistent measurement of motion and acceleration. Newton claimed two time intervals could be judged as equal based on his laws of motion: “the distinction between equal and unequal time intervals is implicit in the distinction between inertial motion and motion under the influence of a force” (DiSalle 20-21), in that “Any measurement of time intervals is necessarily based on the observation of some motion… the laws of motion provided the necessary and sufficient framework for understanding the interactions of bodies in space and time” (DiSalle 20/71). Thus time is measured through motion, but simultaneously, absolute time exists independently of all motion. Newtonian absolute time, on its own, cannot be considered an ontology of time; but metaphysically, the claim is asserted that it is an objective structure. Whilst it can certainly be considered a philosophical approach to time, it is not a complete account, as it “treats space and time solely from the perspective of classical mechanics – that is, as concepts implicitly presupposed by the classical mechanical understanding of causality and force” (DiSalle 55). But the following of Newtonian time is absolutely true: Though he is concerned with the structure of time rather than a complete ontological account of it, this structure is “out there,” part of the world, independent of the observer.

Eleven years before the publishing of the Critique, Kant shifted away from any defense of the Newtonian theory of absolute space and time (Di Salle 63), marking the beginning of his conceiving of them as the forms of inner and outer intuition later presented in the Transcendental Aesthetic. Time, to Kant, was not to be considered as a property belonging to things in themselves:

Time is not an empirical concept that is somehow drawn from an experience. For simultaneity or succession would not themselves come into perception if the representation of time did not ground them a priori. Only under its presupposition can one represent that several things exist at one and the same time (simultaneously) or in different times (successively) (B46/178).

The simultaneity and succession Newtonian time assumes as objectively given in nature can in fact only be perceived because they are grounded in the a priori representation of time. Time’s form is first and foremost explicitly not a derived empirical concept, as such relations of time, like simultaneity and succession, can only be perceived after its presupposition. 

Time then is “not something that would subsist for itself or attach to things as an objective determination, and thus remain if one abstracted from all subjective conditions of the intuition of them” (B49/180), but rather it is “nothing other than the form of inner sense, i.e., of the intuition of ourself and our inner state” (B49/180). Time has a specific subject-dependence; it cannot exist for itself, i.e. objectively on its own as something external as Newton posited, but rather exists only because the subject exists, and it is our mode of inner sense. Time can be represented analogically as an infinite line of one dimension, in which the succession and ordering of temporal relations are illustrated, and which can then “be expressed in an outer intuition” (B50/180). Kant does not rely on the laws of motion to justify the intuitive nature of time, rather time itself can ground any later representation of time (such as time posited by Newton). He reiterates, “Time is therefore merely a subjective condition of our (human) intuition (which is always sensible)... and in itself, outside the subject, is nothing,” (B51/181), a summarial claim directly counter to Newtonian absolutism proclaiming external objective (non-subjective) time. 

Yet, this time is necessarily objective, despite its reliance on the subject “in regard to all appearances” (B51/181). Things do not appear in time but rather the abstraction is made from the intuition of phenomena, which is the mode by which time “belongs to the representation of objects” (B52/181). It is then not objects themselves but rather their appearances that are in time. So, whilst time is empirically real/objectively valid in regard to all phenomena, Kant subtly targets Newton’s assertions in writing 

We dispute all claim of time to absolute reality, namely where it would attach to things absolutely as a condition or property even without regard to the form of our sensible intuition… In this therefore consists the transcendental ideality of time, according to which it is nothing at all if one abstracts from the subjective conditions of sensible intuition, and cannot be counted as either subsisting or inhering in the objects themselves (without relation to intuition)” (B52/181-182). 

Therefore time cannot be claimed to have absolute reality because, as a subject, the relations of time have already been given by the intuition of time. If you abstract from any sensibility, particularly inner sensibility, there can be no time to speak of whatsoever. In such a case, with no observer, things in the universe would simply happen according to no necessary temporal ordering. In the elucidation of the Aesthetic, Kant furthers this reasoning, introducing the empiricist’s counter argument “which concedes empirical reality to time but disputes its absolute and transcendental reality” (B53/182). The claim is that because of the existence of alterations, and alterations are only possible in time, then time must have empirical reality. But, again, this circumvents the initial requisite of sensibility which is that time must already exist as inner sense: “Time is certainly something real [(as the empiricists claim)], namely the real form of inner intuition. It therefore has subjective reality in regard to inner experience, i.e., I really have the representation of time and my determinations in it. It is therefore to be regarded really not as object but as the way of representing myself as object [(as all objects are in time to the observer)]” (B53-54/182). Those absolutists, such as Newton, are dealt one final direct attack in the elucidation of the Aesthetic:

Those, however, who assert the absolute reality of space and time… must themselves come into conflict with the principles of experience… they must assume two eternal and infinite self-subsisting non-entities (space and time), which exist only in order to comprehend everything real within themselves (B56/183-184).

Kant knows that we cannot assert any claims about things in themselves. The absolute reality of time conflicts with the principles of experience because absolutists can only assume the absolute reality of time if they concede that it is a self-subsisting non-entity whose necessity cannot be grounded in experience.

Relativity is an umbrella term that describes both special and general relativity. The theory of special relativity consists of two central claims; firstly, that “the speed of light in a vacuum is the same for any observer, regardless of the observer’s location or motion, or the location or motion of the light source” (DOE). The second is that the “laws of physics are the same for all reference frames that are not speeding up or slowing down relative to each other” (DOE). Differing reference frames, i.e. different observers, perceive space and time differently. The theory of general relativity states “that gravity is how mass warps space and time. The bigger the mass, the more it warps things… Special and general relativity come together to show how time is measured differently in different frames of reference, called time dilation. This effect happens because different frames of reference perceive time and space differently” (DOE). For the sake of understanding, let’s use an example; subject A is moved spontaneously into a point of near-infinite gravity, bringing with them a clock. Subject B exists in an area of gravity similar to that of Earth’s. Subject B observes subject A; from subject B’s point of view, subject A’s clock has slowed to an imperceptibly slow speed, giving the appearance that it has stopped, as has any movement of subject A themselves. In time local to Earth, subject B will continue to age and eventually pass away. Subject A still perceives their own passage of time as “normal;” for each second in their local area, the clock ticks one second forward, but in the area local to subject B, an astronomically large amount of time has already come to pass. Time has not actually stopped for subject A, but the two subjects’ measurements of time differ due to spacetime curvature.

The immediate difficulty upon learning of the existence of relativity is this: Time is affected by objects in space, dependent upon their gravitation. How do we reconcile this with the Kantian notion that time is strictly subjective, in that it is not really “out there” independent of outside influence? In Michael Friedman’s Kant and the Exact Sciences, he articulates this issue more thoroughly:

In Einstein's new theory of gravitation–the general theory of relativity–not only may space (more precisely, spacetime) have a non-Euclidean structure, but space (space-time) in fact has no fixed structure at all independent of the matter and energy distributed therein; and it follows that there is no longer a sense in which the structure of space (space-time) can be viewed as fixed a priori… the idea of a fixed a priori spatio-temporal structure serving as the foundation of the exact sciences and indeed of all human knowledge, can no longer consistently be maintained (Friedman 341).

This argument is certainly convincing; the geometric principles Kant perceived to be universally so in space (e.g. that through a point not on a line, only one parallel can be drawn), as well as the uniform linearity if a singular-dimensional time shared by all observers, appears to be broken by the empirically verified theories of relativity. Spacetime has a non-Euclidian structure, varying from place to place depending on gravity, seemingly not fixed a priori. It certainly seems, at this point, that space and time are closer to the Newtonian absolutes of an observer-independent space and time (though of course the Newtonian principles can be completely discarded, i.e. the proposition of absolute simultaneity). But, an issue in this damning argument arises, particularly in the tangential topic of space. Spatial intuition is the form of outer intuition, and it is the structure of this intuition that, to Kant, is Euclidean. There is then a difference in explanatory level between these two conceptualizations of space and time. The forms of space and time are conditions for experience, not empirical scientific descriptions. Even if empirical space turns out to be non-Euclidian, and time thus not uniformly linear, the two forms are still necessary for human cognition. Thus relativity does not show that there is an objective spacetime in itself, rather that spatiotemporal relations are relative to frames of reference. This distinction, I argue, bolsters the Kantian notion of observer dependence and the subjectivity of time; it just so happens that Kant's claim that time is “nothing more than” an inner intuition needs to be adjusted.

A brief exposition of the philosophical work, particularly by philosophers of science in the wake of the principles of relativity, must now take place. In the early 1920s, Ernst Cassirer published a neo-Kantian work pertaining to the principle of relativity. Cassirer argued “that the general theory of relativity, whose fundamental feature is characterized as having removed from space and time ‘the last remnant of physical objectivity’, has improved on Kant in bringing about the clarification of the role of pure intuition in empirical cognition” (Ryckman 44). The theory provided “‘the most determinate application and implementation of the standpoint of critical idealism within empirical science’” (Ryckman 47-48). The principles of relativity then build on the Kantian notion of intuitive time as observer/subject dependent; this is necessarily how spatiotemporal relations are in a relative temporal structure. Ryckman himself however posits the following counterargument:

Now the scale and clock readings of any particular observer might well be understood as 

the resultant of a synthesis of concepts and intuitions in the strictly Kantian sense of 

constitution. However, relativity theory has shown that, however necessary to cognition 

from a particular ‘point of view’, from the impersonal standpoint demanded by relativity 

theory these can compromise at most ‘relative knowledge’, knowledge that, as observer 

dependent, is not fully objective… the ideal of completely impersonal objectivity that is 

the conceptual core of relativity theory mandates conceptual or functional, rather than 

spatiotemporal, cognitive representation, breaking the confines of the Transcendental 

Aesthetic (Ryckman 186-187).

Ryckman suggests that physics, following relativity, should strive to be generally covariant, i.e. valid for any and all frames of reference, privileging no observer-based time. Physics privileges mathematical and universal representations, not intuition as a cognitive medium. I’m forced to concede that, in the context of modern physics, Ryckman’s assertions are correct in that strictly physical theory transcends the idealism of the Aesthetic. This counterargument though pertains more to the experimental application and principles of modern physics than to the validity of the transcendental idealism Kant proposes. Each observer still experiences time through inner sense; phenomenal experience is still structured spatiotemporally according to the basic forms of time proposed in the Transcendental Aesthetic. In their measurements, physicists still experience measurements in the form of intuitive time.

Thus, the Kantian framework remains the condition of all possible experience. Kantian time and Einsteinian relativity operate on different levels, though these levels are complementary to one another. Relativistic effects can be observed/described/measured only because human cognition is structured temporally by the intuition of time in the first place. Relativity in a sense confirms that time is indeed not “out there” but is observer-dependent, bound to the subject’s mode of intuition; it cannot be read as an ontological structure of the temporality of the world. Newtonian absolute time is assuredly extinguished by the principles of relativity, as time can only be measured in a specific frame of reference rather than in the things themselves. 

Works Cited

Department of Energy. DOE Explains: Relativity. https://www.energy.gov/science/doe-explainsrelativity. Accessed June 2025.

DiSalle, Robert. Understanding Space-Time: The Philosophical Development of Physics from Newton to Einstein. Cambridge University Press, 2006.

Friedman, Michael. Kant and the Exact Sciences. Harvard University Press, 1992.

Kant, Immanuel. Critique of Pure Reason. Translated and edited by Paul Guyer and Allen W. Wood. Cambridge University Press, 1998.

Ryckman, Thomas. The Reign of Relativity: Philosophy in Physics 1915–1925. Oxford University Press, 2005.