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“We come now to metaphysics, a purely speculative science, which occupies a completely isolated position and is entirely independent of the teachings of experience. It deals with mere conceptions—not, like mathematics, with conceptions applied to intuition—and in it, reason is the pupil of itself alone. It is the oldest of the sciences, and would still survive, even if all the rest were swallowed up in the abyss of an all-destroying barbarism. But it has not yet had the good fortune to attain to the sure scientific method. This will be apparent; if we apply the tests which we proposed at the outset. We find that reason perpetually comes to a stand, when it attempts to gain à priori the perception even of those laws which the most common experience confirms. We find it compelled to retrace its steps in innumerable instances, and to abandon the path on which it had entered, because this does not lead to the desired result. We find, too, that those who are engaged in metaphysical pursuits are far from being able to agree among themselves, but that, on the contrary, this science appears to furnish an arena specially adapted for the display of skill or the exercise of strength in mock-contests*—a field in which no combatant ever yet succeeded in gaining an inch of ground, in which, at least, no victory was ever yet crowned with permanent possession.”

*Scheingefechte: sham battles

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The following is a note to the eighth paragraph of the Preface to the Second Edition 1787

The examples of Galileo, Torricelli, and Stahl reveal experiment as a constructed relation in which nature becomes intelligible through the deliberate arrangement of determinate conditions. From the reversible transformation of metal and lime, we see that construction does not fabricate its object but brings together the conditions through which an otherwise hidden relation can become manifest, measurable, and recoverable.

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In “construct,” the prefix “con-” comes from Latin con-, meaning “with,” “together,” or “together with.”

“Construct” comes from Latin construere:

• con- = together
• struere = to pile up, arrange, build

So, literally, construct means something like “to build together” or “to put together.”

The interesting thing is that con- doesn’t always simply mean physical togetherness. It can indicate combination, joining, or bringing things into an organized relation.

You can see the same movement in:

• connect = join together
• combine = put together
• compose = put together
• converge = come together
• congregate = gather together
• constitute = establish or make up together
• consensus = “thinking/feeling together”

And “structure” itself is related to the same Latin root: struere, “to build.”

So “construct” has a remarkably literal philosophical structure:

“con-” → together
“struere” → build
“construct” → build-together / put-together

That makes “construct” different from simply “make.” To construct something implies that elements are brought into a relation with one another.

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STAHL, at a later period, converted metals into lime, and reconverted lime into metal

This is an old chemical/philosophical way of speaking, and the sentence becomes clearer if we look at the terms historically. “STAHL, at a later period, converted metals into lime, and reconverted lime into metal”

Here “lime” does not mean the citrus fruit. In older chemistry, “lime” meant what we would now generally call a calcined oxide: a substance produced by strongly heating a metal or mineral.

Georg Ernst Stahl (1660–1734), associated with the phlogiston theory, treated metals as composites that could undergo a reversible transformation. In simplified form:

metal → calcined metal (“lime”) → metal

For example, heating a metal in air could produce what appeared to be an earthy, powdery substance. That was called the metal’s “calx” or “lime.” Later, certain processes—especially heating it with carbon or another reducing substance—could restore the metallic form.

The important conceptual point is that Stahl was not merely saying that one substance disappeared and another appeared. He was trying to understand transformation: how something apparently loses its metallic character and then can recover it.

And this connects beautifully with the question about “construct.” The Latin con- means “together,” while struere means “to build.” A “construct” is therefore something whose identity arises through an arrangement or composition of elements. Stahl’s chemistry is working with a similar intuition: the visible form of a thing can change while something underlying the transformation is preserved or redistributed.

Historically, though, Stahl explained this through phlogiston, which modern chemistry rejected. The modern interpretation would describe many such transformations through oxidation and reduction rather than the gain or loss of phlogiston.

And that phrase — “loses its metallic character and then can recover it” — points toward something deeper than the particular chemistry.

When a metal is calcined, it seems to undergo a strange ontological change. The metal is still materially implicated in what remains, but the recognizable properties by which we called it “metal” have disappeared. It becomes dull, earthy, brittle, powdery: a “lime” or calx. Then, through reduction, the metallic character returns. The metal appears again.

So there are two ways of interpreting what happened.

The naive interpretation is:

metal → destruction → new substance → reconstruction of metal.

But the older chemical problem is more interesting:

metal → altered state → metal.

The question becomes: what persisted through the transformation such that the second metal can be understood as a recovery rather than an entirely new creation?

This is one reason the history of chemistry is philosophically fascinating. “Substance” begins to separate from “appearance.” What makes something metal cannot simply be identical with its immediate visible properties, because those properties can disappear while the material can enter a process through which they reappear.

And there is an even stranger point: the “lime” is not simply an absence of metal. It is a positive state produced by a transformation. The metallic character is absent, but the absence is operative. Something has happened to the metal that prevents it from appearing as metal, and another operation can reverse that condition.

So instead of thinking:

“metal disappears”

we might say:

“metal enters a condition in which its metallic character is no longer manifest.”

Then reduction does not necessarily “create metal from nothing.” It removes or reverses the condition that prevented the metallic form from appearing.

That distinction is very close to the problem you’ve been developing around absence: an absence need not be mere nothingness. The metallic character can be absent from appearance while the process that governs its return is still materially effective.

The modern chemical status of Stahl’s “metal → lime → metal” transformation: it is understood very well now, but in a completely different theoretical framework from Stahl’s.

For a typical metal, the sequence is essentially:

metal + oxygen → metal oxide (“lime”/calx)

and then:

metal oxide + reducing agent → metal

For example, with copper:

2Cu + O₂ → 2CuO

and then, under suitable reducing conditions:

2CuO + C → 2Cu + CO₂

So what Stahl interpreted through phlogiston theory we now understand principally through oxidation and reduction. The metal has combined with oxygen; reduction removes the oxygen from the oxide, restoring the metallic state.

But the philosophical feature you noticed remains. The metal has not simply gone from “being” to “non-being.” Its organization and chemical relations have changed. What we call its “metallic character” depends on its chemical state. In the oxide, the same element is present, but it is participating in a different structure and therefore exhibiting radically different properties.

This is why the modern formulation is actually rather elegant:

metal → oxidation → oxide → reduction → metal

The transformation is reversible under appropriate conditions because the underlying chemical constituents have not simply been annihilated. They have been rearranged.

And this is precisely where Stahl’s mistake becomes historically important. Phlogiston was wrong as a chemical theory, but the phenomenon that motivated the theory was real: combustion and calcination involve a transformation in which something apparently loses a defining property and can subsequently recover it. Chemistry eventually explained that transformation not through an invisible substance leaving the metal, but through changes in its relation to oxygen and other substances.

The important word is “defining.” If we say that a piece of iron is metal because it is shiny, conductive, malleable, metallic-looking, etc., then oxidation creates a philosophical problem. The iron can cease to exhibit many of those properties without the iron itself ceasing to exist. The “metal” seems to disappear, but the element has not simply vanished. It has entered another chemical relation.

So there is a distinction between the persistence of something and the persistence of its character.

Iron can remain present while “metallicity,” as a recognizable mode of being, is suspended. The oxide is not merely failed iron. It is iron in a different chemical organization. Then reduction can restore the metallic condition.

This gives us a very interesting sequence:

presence → withdrawal of a characteristic → transformation → restoration of the characteristic.

And notice that the “withdrawal” is not nothing. The absence of metallicity has a cause and a mechanism. Oxygen has combined with the metal; the resulting structure has different properties. The absent property is therefore being actively maintained by a material relation.

That is perhaps more precise than saying that the metal “loses” its metallic character. It undergoes a transformation in which one regime of properties gives way to another.

And this is where the old language of “lime” becomes philosophically suggestive. The calx looks like the corpse of the metal: the metallic appearance is gone, yet the metal has not simply become nothing. Then the possibility of reduction reveals something strange: what looked like an irreversible disappearance was actually a reversible transformation.

The modern chemist would not say that “metallicity” is an independent substance hiding behind the oxide. But the phenomenon still forces us to distinguish between what is present materially and what is present as a particular form, property, or organization.

That distinction becomes extremely powerful if you are thinking about absence. The absent thing may not be an absent object. It can be an absent determination of something that remains present. And because the determination has conditions, its absence can itself be causally effective.

The metal is there.

The metallic character is not.

And yet the absence of that character is not inert, because the chemical state that excludes it can itself be acted upon.

GALILEI experimented with balls of a definite weight on the inclined plane, when TORRICELLI caused the air to sustain a weight which he had calculated beforehand to be equal to that of a definite column of water, or when STAHL, at a later period, converted metals into lime, and reconverted lime into metal, by the addition and subtraction of certain elements

The passage is describing a transformation in the very meaning of “experiment.” These experiments are not merely observations of nature. They are constructed situations in which a quantitative or reversible relation can be made to appear.

Galileo places a ball of definite weight on an inclined plane and observes its motion. Torricelli establishes that the atmosphere can sustain a column of mercury whose weight corresponds to the pressure of the surrounding air. Stahl transforms metal into calx and then restores the metal through chemical operations. In each case, something that might otherwise remain obscure becomes intelligible because the investigator establishes a controlled relation: weight to motion, atmospheric pressure to a column of liquid, chemical composition to the transformation of a substance.

The common structure might therefore be expressed as:

something given → controlled intervention → determinate transformation → reversibility or quantitative correspondence → intelligible law

But there is an important progression in the examples. Galileo isolates motion. Torricelli isolates pressure. Stahl isolates composition and transformation. The experiment increasingly ceases to ask simply, “What happens?” and instead asks, “Under what conditions does this transformation occur, and can I produce it again?”

That is why the phrase “by the addition and subtraction of certain elements” is especially important. Stahl’s experiment turns chemical transformation into an operation. The investigator does not merely watch metal become lime. He can intervene in the process and reverse it. The transformation becomes something that can be reproduced, controlled, and theoretically articulated.

So if we wanted to give the whole passage a single conceptual summation, I would put it this way:

Experiment becomes the construction of a determinate relation in which nature is made to disclose a rule through controlled transformation.

And there is a subtle philosophical consequence. The experiment does not simply reveal an already visible object. It produces a situation in which something invisible or indeterminate becomes legible through its effects. The pressure of air is not itself seen; its effect is measured by the column. The chemical relation responsible for the transformation is not simply seen; it is disclosed through the reversible conversion of metal and calx. The law emerges through the intervention.

That is very close to the deeper significance of the passage: modern experimental science increasingly understands nature not as something passively contemplated, but as something whose determinate relations can be elicited through a carefully constructed encounter.

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Taken together, the note gives the word “construct” a much more precise significance within Kant’s passage. The examples of Galileo, Torricelli, and Stahl are not merely examples of successful experiments; they show progressively what it means to construct an object of scientific cognition. In each case, something is placed into a determinate relation by an intervention, and that relation makes possible a knowledge that could not be obtained through passive observation alone. The ball, the atmospheric pressure, and the metal are not simply “there” as objects waiting to be looked at. They become scientifically intelligible through the construction of conditions under which their relations can be determined.

This makes the etymology of “construct” particularly useful, provided it is not allowed to carry more historical weight than it actually can. Con- and struere give us the suggestive sense of bringing or building together, but Kant’s philosophical use of “construct” has a more technical mathematical meaning: to exhibit a concept in intuition, especially through the construction of a corresponding object. Nevertheless, the broader semantic intuition remains valuable. Construction does not mean arbitrary fabrication. It means that elements are brought into a determinate relation such that something becomes available to cognition.

Stahl is especially important because his example makes the structure of construction almost impossible to overlook. The metal becomes lime and the lime becomes metal through the addition and subtraction of elements. What initially appears to be the disappearance of one thing and the emergence of another becomes a controlled transformation. The experimentalist discovers that what appears as a change of substance can be treated as a determinate relation among constituents. The “thing” is therefore no longer understood merely according to its immediately given appearance. Its identity becomes intelligible through the operations by which its state can be altered and, under suitable conditions, restored.

This gives the three examples a striking sequence. Galileo establishes a relation through motion; Torricelli establishes a relation through equilibrium; Stahl establishes a relation through transformation. In each instance, the decisive question is not simply what is present before observation, but what can be made to occur under determinate conditions. The experiment therefore moves from the given toward the condition of its determination. We do not merely receive the phenomenon; we arrange a situation in which a particular relation can disclose itself.

And this brings the chemical example directly into the problem of absence. When metal becomes oxide, metallicity disappears as an immediately manifest determination, but what has disappeared is not thereby nothing. The absence of metallicity has a material condition. Oxygen has entered into a particular relation with the metal, and that relation maintains the altered state. Reduction can then reverse the relation. Thus the absent determination is itself intelligible through the conditions that sustain its absence and the operation that removes those conditions.

The important conceptual movement, then, is not simply:

metal → oxide → metal

but:

appearance → withdrawal → determinate condition → intervention → restoration.

That is a stronger formulation because it does not treat absence as annihilation. Something can cease to appear under one determination while remaining involved in a structure through which that determination can be recovered. Stahl’s example therefore gives experimental form to a distinction between presence and determination: what is present need not be present in the same way.

And now the Kantian passage becomes considerably sharper. When Kant says that “reason must approach nature with its principles in one hand, and with experiment which it has devised in the other,” the experiment is not an arbitrary disturbance imposed upon nature. It is the construction of a situation in which nature can answer a determinate question. Galileo’s inclined plane, Torricelli’s column, and Stahl’s chemical transformations all exemplify this. Nature is not simply asked to speak; conditions are constructed under which a relation can become answerable.

The summation of the note could therefore be: construction is the bringing-together of conditions through which what is otherwise merely given becomes determinately intelligible. Experiment is construction in this practical sense. It constructs the relation, not the truth arbitrarily; and because the relation can produce, reverse, or reproduce a transformation, the phenomenon becomes something that can answer to reason.

This also explains why Stahl is such a powerful final example. The conversion of metal into lime and lime back into metal is almost a miniature model of the experimental method itself. The investigator does not merely encounter a transformation. The transformation is produced, its conditions are modified, and its reversal is attempted. What was initially a mysterious alteration of appearance becomes a determinate sequence of operations. The experiment thereby turns disappearance and recovery into something intelligible.

The deeper issue, then, is not that science “constructs reality” in the sense of simply inventing it. Rather, science constructs the conditions under which a particular determination of reality can become manifest. The object is given, but its intelligible relation is elicited. And that distinction may be exactly what the eighth paragraph needs: construction is neither passive reception nor arbitrary fabrication, but the organized bringing-together of conditions through which nature is compelled to disclose a rule.