Kant's work in "Critique of Pure Reason" aims to "establish" a "kingdom of empirical natural necessary scientific knowledge," asking how such a "kingdom" is possible? What is the "basis" of its "facts"? And what is the "basis" of "rights"? Kant clearly distinguishes between the issues of "de facto" (fact-based) and "de jure" (rights-based); if readers do not pay attention to this distinction, it is difficult to enter Kant's philosophy.
Kant does not deny that all knowledge originates from the materials provided by the senses; without sensory "stimuli," "knowledge" could never arise. However, under Hume's meticulous analysis, the combination of materials provided by the senses can only yield a kind of common-sense habitual and therefore subjective universality, rather than necessity. Hume certainly recognized that logic and mathematics possess a necessity that does not depend on sensory experience, but they also only have subjective necessity and lack objectivity. In this regard, Kant's "critical philosophy" aims to combine the two, that is, to "establish" an "objective necessity," thus making it possible to "construct" a "kingdom of knowledge science"; otherwise, the "territories" that Hume has "divided" would be in disarray.
Thus, the key to "unifying the territory" lies in the fact that this "kingdom" must exist under a "unified" "law" and "regulations," where various "factors" "properly" position themselves and "coexist" under the "same law." While "empirical sensory experiences" may be "different," in terms of "rights," they are under the "same law" of "governance and regulation." In this way, the problem of "one" and "many" that has existed since ancient Greece can be resolved within the "kingdom of knowledge."
Kant's point is that the "materials" provided by the "senses"—the "sensations"—are indeed a necessary condition for "knowledge." They provide "stimuli" to the "senses," but they cannot provide "regulations" for these materials. "Sensory experience" is "factual," while the rational cognitive function is "decisively regulatory": the former is "factual," and the latter is "juridical." "Facts" are "empirical," while "juridical" does not rely on experience; Kant, following Hume, also refers to them as "a priori." These two "factors" combine within a "unified" "territory"—the kingdom of scientific knowledge—where these "a priori" rational cognitive functions exert "regulatory" influence, making this "knowledge" not only a "habitual" "convention" but also "necessary." Thus, Kant's advancement of Hume's work lies in the assertion that "empirical knowledge" is not merely "empirical habits," but also possesses "a priori necessity," meaning that within "experience," there are also "a priori" factors that do not depend on experience, and these "factors" are "decisively regulatory." In this sense, the "empirical knowledge" governed by "a priori" regulations is called "transcendental knowledge," which possesses "objective (factual object) necessity," and thus is "scientific knowledge."
Through what do those "a priori" "factors" exert their "transcendental" influence? Through the "legislative" function of "experience." The "intellect" legislates for "nature," allowing the "reverence" for "nature" to be "regulated," making what is originally "synthetic" in "experience" also possess "a priori" characteristics, while also making what is originally "analytic a priori" in "logical forms" also possess "synthetic" characteristics. This is where the creative significance of Kant's question, "How is a priori synthetic judgment possible?" lies. The "intellect," through its legislative power over "natural experience," ensures that "a priori synthetic judgments" not only have an "objective basis" in empirical fact but also have a "basis" in "juridical law," thus providing "maintenance" and "promotion" for the development of "scientific knowledge."
However, although the "territory" of the "kingdom of scientific knowledge" is "infinite" in "empirical facts," it is "limited" in "juridical rights." This means that the "legislative power" of the "intellect" is "restricted," and this aspect needs careful examination. What does it mean to be "infinite" in "empirical facts"? It means that the "legislative power" of the "intellect" is allowed to expand infinitely in "space" and to "extend" infinitely in "time"; however, it does not allow "expansion" beyond "time and space."
This point is significant in Kant and even in the entire German classical philosophy.
In Kant, "time and space" seem to be a "gateway" for the "kingdom of scientific knowledge," where the materials provided by the "senses" enter this "kingdom" with a "legitimate" identity, making it possible to be organized and constructed into a "necessary" "(theoretical) system" according to the "laws" established by the "intellect." However, this "gateway of time and space," while "intuitive," is also "a priori," meaning it does not depend on "experience," and thus "time" and "space" themselves, like the "conceptual categories" of the "intellect," are merely some "(a priori) forms." Therefore, the combination of the two "a priori forms" (intuitive and conceptual) makes "a priori synthesis" possible, within which the "intellect" "legitimately" exercises its "legislative power."
However, beyond this "intuitive" "scope" of "time and space," the "intellect" has "no power to legislate." From an epistemological perspective, the "a priori" "conceptual categories" it employs are only "allowed" to be applied within the scope of "empirical intuition," that is, "within time and space."
"Within" "time and space," this is the "limit" of the "power" of "intellectual legislation"; "beyond" this limit, the "conceptual categories" of the "intellect" are not allowed to exercise their "legislative power." The work of "critical philosophy" is to delineate this "boundary," "restricting" the "legislative power of the intellect" to "within time and space," preventing the "intellect" from "overstepping."
Why does the "intellect" have a tendency to "overstep"? The "intellect" that has not undergone "critical examination" does not clearly understand its own "legislative" "authority," mistakenly believing it has the right to legislate for all "objects," and because it lacks the capacity for "intuition," it can only rely on the "senses" to provide the materials for "objects" within the realm of "knowledge experience." Thus, these "objects" must be tangible and intuitive things "in time and space." As for those simple "thought entities" or "concepts" that are "not in time and space," such as "free will," "immortal soul," and "God," they have no "instances" of "proof" or "verification" in "time and space," and the "intellect" has no right to place them within its "juridical" realm and construct them into a "necessary" "scientific knowledge." The first task of "critical philosophy" is to "draw a clear" boundary to prevent the "intellect's" "overreach," believing itself capable of "transcending" this boundary to reach the "transcendent" "territory." The work of "critical philosophy" shows that the "legislative power" of the "intellect" is only effective within the realm of what can be experienced and intuited.
However, although "critical philosophy" has clearly established such a "boundary," it also recognizes that the "intellect's" tendency to "overreach" is often an "unstoppable" "natural inclination," stemming from the fact that the "intellect" itself lacks the capacity for "intuition." It always assumes that anything that is "non-contradictory" in "thought" is "truth," without needing "verification" from "facts." In reality, any "necessity" of "scientific truth" must be a mutual agreement between "subjective (conceptual)" and "objective (actual objects)."
The "intellect" can indeed "think" these "transcendent" "representations" without contradiction, but if it assumes that these "representations" are also "facts" within "experience," and thus are some "intuitive" "objects," it will "foolishly" believe that these "thought entities" are like all things in the world, which leads to the "contradictory" situation being destroyed by the "overreach" of the "intellect," falling into "antinomies." In this sense, "antinomies" serve as a "punishment" for the "intellect's" "overreaching arrogance."
However, the "overreach" of the "intellect" is also an "unstoppable" tendency of its "freedom." The "intellect" originally belongs to "reason," is "independent," and thus is "free." However, in order to "establish" a "necessary kingdom" within the realm of "empirical nature," it will be constrained by "objects" that are "different from itself," and its "legislative" scope will be limited by "external spatial phenomena" (physical natural phenomena) and "internal temporal phenomena" (psychological phenomena). As for the "a priori independence" and "freedom" of the "intellect" itself, it has no "legislative power," because within an "(independent) kingdom," the "legislator" must legislate for an "other" "object" to be comprehensive and substantial, rather than merely formal. Therefore, when the "intellect" "thinks" about the "essence" of an "object itself," it can only be an "empty form." Once it tries to treat those "ideas" of "objects themselves" as "experiences" and "phenomena" to grasp scientifically, it will become "self-contradictory." In this sense, the "intellect" in the "kingdom of empirical science" possesses only "formal" "freedom," while being "restricted" in "substantial sensory materials" (by intuitive time and space).
However, the "tendency" of the "intellect" to "overreach" in the "kingdom of knowledge" is not only constrained by "time and space" conditions but also receives "regulations" from "reason" in "practice." In this sense, the "freedom" of "practical reason" is not only "formal" but also "regulated and substantive." The "practicality" of "reason" ensures the "reality" of "freedom."
This means that "reason" legislates for "(will) freedom" in "practice," providing "regulations" for "freedom," just as the "intellect" legislates for "nature" in "theory"—providing "regulations" for "nature."
The "intellect" legislates for "those in time and space," providing "regulations" for "nature"; "reason" legislates for "those beyond time and space," providing "regulations" for "freedom."
"Those limited by time and space" are "necessary" in "theory," while "those not limited by time and space" are "free" in "practice": the former establishes the "kingdom of scientific knowledge" for the "intellect," while the latter establishes the "kingdom of moral practice" for "reason."
In this sense, "freedom" is not "lawlessness," and "those not limited by time and space" are not "fantastical." On the contrary, these "unlimited and unrestrained" entities are only unbound by "time and space" conditions, but rather "follow" the "laws" established by "reason" for their own freedom. "Self-legislation and self-obedience" is the highest meaning of "law," and is a "necessity of transcendent freedom" that is stricter than the "necessity" of "natural time and space"—perhaps what was called "fate" in ancient Greece.
We see that due to the legislative function of "practical reason" for "transcendent beings," the "overreaching" "intentions" of the "intellect" exercising "legislative power" in "theoretical reason" are "guided" and "led," allowing it to "settle" into its duties, continuously striving without restriction to explore the "mysteries" of "nature," exercising its power in the "vast expanse" of "time and space," and taking the "ultimate purpose" set by "practical reason" as an "ideal" to "constantly" approach. This "guidance" directs the "development" of the "intellect," and with this "goal" and "direction," all human labor can be said to be "progress."
The "ultimate purpose of the highest good" posited by "practical reason" is, in the context of the "kingdom of knowledge," an "ideal" that transcends time and space, but in the context of the "kingdom of morality," it possesses "reality," because "the will of practical reason" inherently means "to" realize a "purpose." Although the "purpose" has not yet been "realized," it is "set" for the sake of "realization." The "empirical purposes" within "time and space" are thus, and the "ultimate purpose" beyond time and space is likewise. "Reason" acknowledges the "reality and objectivity" of the "ultimate purpose," just as the "intellect" confirms that "empirical purposes" must always be "realized" within "time and space." Moreover, the "intellect" must also acknowledge that there are "purposes" that "cannot be realized," because the "categories" of the "intellect" include "contingency"; however, since "reason" legislates for itself, the direction of the "law" is without exception, and the "reality" of the "ultimate purpose" beyond time and space is also "absolutely necessary."
Thus, although people cannot find "examples" of the "ultimate purpose of the highest good" in the "vast space" and "long river of history," they still have the "right" to "believe" in the "existence" of this "ultimate purpose of the highest good."
How to understand "practical reason's" "certainty" regarding the "ultimate purpose of the highest good," this "hypothetical postulate," is an important task of Kant's "Critique of Practical Reason." Kant's work points out that this "certainty" comes from a different kind of "proof" than "scientific knowledge," and is not merely reliant on the "deduction" of "concepts," but is a "promise" made by "practical reason" itself: that people "have the right" to "hope" for "something." This "something," as the "moral freedom purpose" of "practical reason," although lacking "reality" in the "empirical world of sensory experience," exists in the "realm" of "transcendent thought entities," where through the "practical legislation" of "reason," "freedom" receives "concrete" "regulations," thus also having its own "object"; this (these) "objects" possess their own "regulatory characteristics," and in this sense, also have "reality" in terms of "purpose" and "certainty," not merely as "forms" of "thought."
In this sense, the "objects" of "practical reason" are also self-"set," just as in the "realm of knowledge," the "conditions" of "experience" are such that "the intellect" makes "empirical objects" possible, and "rational freedom" also makes the "moral" "object"—the "ultimate purpose of the highest good"—possible; only that in the "realm of knowledge," its "objects" must be "within" "time and space," while the "moral practice" "object" of "reason"—the "highest good"—is always "beyond" "time and space." The so-called "within time and space" and "beyond time and space" merely indicate "accepting or not accepting" the "constraints" of "time and space conditions," rather than implying that there exists a "heaven" or "hell" that is opposed to the "world of experience." This is the philosophical route that Hegel later took: "finite and infinite," "necessity and freedom," "knowledge and morality," "theoretical reason and practical reason" are of the same identity, rather than having an "infinite" that is opposed to the "finite."
In fact, Kant has already recognized the issue of "communication" between the two "independent legislative" "kingdoms" of "intellect" and "reason." In "Critique of Pure Reason," he has "reserved" space for "practical reason," and in "Critique of Practical Reason," he points out the "priority" of "practical reason" over "theoretical reason," meaning that "theoretical reason" cannot influence "theoretical reason," but "practical reason" can "influence" "theoretical reason." This can be understood as: the "ideals" established by "practical reason" can serve as "guidelines" for "theoretical reason," and "morality" should "guide" the "direction" of "knowledge."
From this, we can further say that "beyond the conditions of time and space," the "guiding" and "normative" aspects influence those constrained by "time and space conditions." This line of thought is further confirmed in Kant's "Critique of Judgment."
"Critique of Judgment" faces a specific individual world, where the "universal" "laws" have already been resolved in "Critique of Pure Reason," while how those "individual" things can be "lawful" is something the "kingdom of knowledge" can only attribute to "contingency." Just as in this kingdom, the "congruence" of "virtue" and "happiness" is merely a "fortunate" "coincidence," only in the "ultimate good" of "practical reason" (beyond time and space) does this "congruence" possess "necessity."
What "Critique of Judgment" seeks to resolve is precisely how this originally humanly diverse "contingent" "pleasure" is not merely a "sensation" and an "arbitrary" "teleological judgment."
Here, we want to particularly emphasize: those judgments that never detach from "specific individual things," that is, how can one also make a "judgment" about those things that cannot detach from "time and space conditions," and like "knowledge judgments," "demand" universal recognition.
This means that for "sensory" "specific individual objects" "in time and space," people also have the right to make "universal, transcendent, and independent of time and space conditions" "intellectual" "judgments."
"Aesthetic judgment" never detaches from sensory intuition; artworks also have concrete factors, which are of course, in principle, "restricted by time and space conditions." However, what "aesthetic judgment" seeks to "judge" is not the "objective attributes" of "specific objects" (according to "intellectual legislation") "in time and space," but rather the "subjective states" of these "objects" in relation to "various intellectual abilities." Therefore, it is not about making "regulations" for the "objects," but about making "reflections"; and the "reflections" made by "judgment" on these "objects" also have their own "a priori legislative" "basis," although this "basis" is not in the "intellect," nor in "reason," but in the "judgment" itself as an "intellectual ability."
This means that "reflective judgment" cannot "borrow" its "laws" from the "intellect" legislating for "things in time and space," nor can it "borrow" "laws" from "reason" legislating for "transcendent" things, but can only legislate for itself through "judgment," and these "laws" apply to the "judgments" made about "specific objects" based on the relationships among "various intellectual abilities"—including "intellect, reason, and imagination." These "objects" are certainly "intuitive," but "reflective judgment" does not make "judgments" based on the actual "time and space" conditions of this thing; rather, it "virtualizes" and "internalizes" it through the "coordinated" relationships among "various intellectual abilities," as if they are "parasitic" within the "kingdom of intellect," without "considering" the actual "time and space conditions" of the thing, thus "driving" these "objects" into "reason" and "endowing" them with "moral" "meaning." Hence, Kant states that "beauty" is the "symbol" of "morality."
This means that although we cannot find the "actual existence" of the "ultimate purpose of the highest good" in the "phenomenal world" of the "kingdom of knowledge," we can "see" this "symbol" of the "infinite ideal of the ultimate purpose of the highest good" in "aesthetic art," within the "purposiveness" of the vast world, even though this "symbol" cannot receive "objective proof" or "verification" from "scientific knowledge," but is merely a "subjective" "cultivation" and "nurturing," a kind of "appreciation," which greatly aids in assisting the "moral ideals" to "guide and promote" the "permanent expansion" and "continuation" of "scientific knowledge" in "time and space."