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idea of particular cases of causal connections. Because an event has always
been followed by another, we come to believe that every event similar to the
first will always be followed by an event similar to the second. But in truth,
no amount of evidence provided by our memory and senses is sufficient to
justify such a belief.8
According to Hume, our belief in the universal causal principle is just a
generalization of our particular causal beliefs. Associating to every per-
ceived event or state of affairs the vivified idea (and thus the belief in the
existence) of a preceding or succeeding event similar to those that have
always preceded or succeeded it, just is entertaining the general belief
that ˜˜everything that comes into existence must have a cause.™™ Thus
Hume derives our representation of causal connections from the
repeated succession of similar events, and our belief in the universal
causal principle from the generalization of our belief in particular causal

Hume, Treatise, p. 167.
Treatise, bk I, part iii, 2“14; Enquiry, sections 4“7.
See Treatise, bk I, part iii, section 8, pp. 104“5; section 14, p. 172. One may wonder whether
Hume actually accounts for the universal principle as he has first introduced it (i.e. the
principle admitted both in metaphysics and by common understanding: ˜˜every beginning
of existence must have a cause™™), or rather gives an explanation of some broader principle
such as: ˜˜every beginning of existence must have a cause and an effect.™™ Many of Hume™s
formulations, throughout the Enquiry and the Treatise, do not give precedence to cause over
effect in the ideas imagination naturally associates with any given event or state of affairs.
The privilege given to the principle as stated can probably be explained more thoroughly
by looking into Hume™s explanation of what he calls ˜˜the world of judgment™™ (Treatise, p. 74,

In the Introduction to the Critique of Pure Reason, Kant states that
accepting Hume™s account would amount to giving up the very content
of the concept of cause:
[In the proposition: ˜˜every alteration must have a cause™™], the very
concept of a cause so obviously contains the concept of a necessity of
connection with an effect and a strict universality of the rule that it would
be entirely lost if one sought, as Hume did, to derive it from a frequent
association of that which happens with that which precedes and a habit
(thus a merely subjective necessity) of connecting representations arising
from that association. (B5)

The charge may strike us as bizarre: after all, as I just explained, the
whole point of Hume™s psychological derivation of the concept of cause is
to account for the idea of necessary connection ˜˜contained in the concept
of cause,™™ and to explain how we tend to inflate mere observed regular-
ities into ˜˜strictly universal rules.™™ Kant is of course aware of this. What
we must take him to mean, then, is that accepting Hume™s account of
precisely these features would be giving up the concept of cause alto-
gether, because it would mean that as far as objects are concerned, our
idea of causal relation can be reduced to the idea of a non-causal relation:
repeated succession of similar events or states of affairs. The ideas of
˜˜necessity of connection™™ and ˜˜universality of the rule™™ would remain
grounded only in the subjective propensities of our mind. Now, one way
to reject such a reduction is to show that Hume in fact does not give an
accurate account of what we actually think when we think ˜˜the necessity
of connection with an effect™™ and the ˜˜strict universality of the rule™™
contained in the concept of cause. This is indeed what Kant will set out
to show. But what does he himself mean by the ˜˜strict universality of the
rule™™ contained in the concept of cause?
I suggest that we find the beginning of an answer to this question in
the preface to the Prolegomena to Any Future Metaphysics. There Kant
credits Hume with having challenged our reasoning capacity to explain
˜˜by what right she thinks anything could be so constituted that if that
something be posited, something else also must necessarily be posited;
for this is the meaning of the concept of cause.™™10 This question concerns
the second aspect of the problem of causality as defined earlier, namely,
cf. Enquiry, p. 26) namely our belief in the existence of independently existing objects. My
purpose here is not to submit Hume™s account to critical scrutiny, but only to lay out its
overall structure insofar as it should help clarify Kant™s own formulation of ˜˜Hume™s
Prolegomena, AAiv, p. 257.

what is the justification of any particular statement of causal connec-
tion?11 However, the terms in which Kant formulates this question are
quite bizarre, and certainly not Humean: to say that something is the
cause of something else is to say that ˜˜if this something is posited, then
something else must also necessarily be posited.™™ It is the word ˜˜posited™™
that intrigues me here. What Kant credits Hume with, is perhaps
Hume™s problem. But this problem is not stated in Hume™s language.
The language is actually that of the hypothetical syllogism in modus
ponens as defined in the logic textbooks of the time. Indeed, Kant™s
phrasing (˜˜if something is posited, something else also must be posited™™)
reproduces, almost word for word, Christian Wolff™s description of the
inference in modus ponens in a hypothetical syllogism:
x407: If, in a hypothetical syllogism, the antecedent is posited, the con-
sequent must also be posited [si in syllogismo hypothetico antecedens ponitur,
ponendum quoque est consequens].
x408: The antecedent being posited in the minor, the consequent should
also be posited [posito antecedente in minore, ponendum quoque est

In a hypothetical judgment (˜˜If A is B, then C is D™™), the ˜˜if™™ clause is
called the antecedent, the ˜˜then™™ clause is called the consequent. In a
hypothetical syllogism whose major premise is ˜˜If A is B, then C is D,™™
the antecedent of the hypothetical judgment being posited, i.e. asserted,
in the minor premise (˜˜A is B™™), then the consequent should also be
posited, i.e. asserted, in the conclusion (˜˜so, C is D™™).
By presenting the problem of causality in these terms, Kant brings
attention to the fact that the problem of how we can think a particular
causal connection turns out to be the following: how can the relation
between two empirical states of affairs be such that the first can be
thought under the antecedent, the second under the consequent of a
hypothetical judgment that functions as the major premise in a syllogism
in modus ponens, such that ˜˜the antecedent being posited (as the minor
premise), the consequent must be posited (as the conclusion)™™? If this is
correct, the ˜˜strict universality of a rule™™ thought in the concept of cause is
the strict universality of the hypothetical judgment (˜˜If A is B, then C is D™™)

See above, pp. 147“8 and n. 5.
Christian Wolff, Philosophia rationalis sive Logica. I do not mean that Kant™s ˜˜universality of
the rule™™ is the universality of the rule of modus ponens itself. The ˜˜universality of the rule™™ is
the universality of the hypothetical judgment, which is the major premise of the hypothe-
tical syllogism in modus ponens. I shall say more on this in a moment.

that we implicitly presuppose as a premise whenever we represent two
particular states of affairs ˜˜A is B™™ and ˜˜C is D™™ in such a way that ˜˜A is B™™
being posited, ˜˜C is D™™ should also be posited.13
One might wonder what the question thus reformulated still has in
common with ˜˜Hume™s problem.™™ But Hume too moved from the ques-
tion of how we think the necessary connection between two events to the
question of how we make the representation of a mere repetition of
similar sequences of events into the representation of a strictly universal
rule or law, in such a way that all future events similar to the one identified
as a cause should be followed by events similar to the one identified as the
effect. What is interesting about Kant™s formulation is that from the outset
it collapses together the two steps in Hume™s analysis of the problem of
particular causal connection. ˜˜If something is posited, something else
should be posited™™ can mean both that the second ˜˜something™™ necessarily
comes to existence if the first does, and that they are, in effect, respectively
thought under the antecedent and under the consequent of a strictly
universal rule. Hume argued, of course, that not reason, but imagination
(the natural propensity of the mind to form the enlivened idea of the
second upon perceiving the first) is the author of the ˜˜strict universality™™ of
the rule. Kant wants to argue that understanding and reason are at work
in universalizing the connection between what precedes and what follows.
Presenting the problem in the terms borrowed from Wolff™s hypothetical
syllogism helps to bring this out.
But what might Kant mean by the ˜˜strict universality™™ of a hypothetical
judgment? When Kant explains the quantity of judgments, he always gives
examples of categorical judgments “ all, some, one A are/is B. What could
be the universality of a hypothetical judgment “ if A is B, then C is D?
Before considering this problem, we need to say more about the hypothet-
ical form itself. Kant™s hypothetical judgment is quite different from our

In addition to the striking similarity between Wolff™s formulation of the rule of modus
ponens and Kant™s presentation of ˜˜Hume™s problem™™ in the preface to the Prolegomena, we
have other reasons to suppose that Kant had the inference in modus ponens in mind.
Already in his pre-critical Reflections on Metaphysics he characterized the problem of
the causal connection in terms of what he called a synthetic respectus rationis ponentis (see
Reflexion 3753, AAxxvii, p. 283 ). And of course in the first Critique and in the Prolegomena
he relates the category of cause to the form of hypothetical judgment. In the Lectures on
Metaphysics contemporary with the Critique, he gives a more detailed exposition of the
relation between the cause and the antecedent, the effect and the consequent of a
hypothetical judgment (see Metaphysik Volkmann, AAxxviii“1, p. 397). For more on this
point see above, ch. 5, pp. 129“31.

material conditional, in two respects: the nature of the connective, the
nature of the propositions connected. I shall consider each in turn.
First, the connective. In our material conditional, the meaning of the
connective is given by its truth table: the conditional (˜˜if p, then q™™) is false
just in case its antecedent is true and its consequent false; it is true in all
other cases. Not so for the connective ˜˜if . . . then™™ of the hypothetical
judgment, which Kant calls Konsequenz (not to be confused with the
˜˜then . . . ™™ clause, called the consequent in English, die Folge in
German). The truth value of the hypothetical judgment does not
depend on the truth value of its components, but on the truth of the
Konsequenz itself: the hypothetical judgment is true just in case there is
between antecedent and consequent a relation of Konsequenz, i.e. a rela-
tion of ground to consequence. Here is what Kant writes in the Jasche ¨
The matter of hypothetical judgments consists of two judgments that are
connected with one another as ground and consequence. One of these
judgments, which contains the ground, is the antecedent (antecedens, prius),
the other, which is related to it as consequence, is the consequent (conse-
quens, posterius), and the representation of this kind of connection of two judgments
to one another for the unity of consciousness is called the consequentia [my
emphasis] which constitutes the form of hypothetical judgments [ . . . ]
In [a hypothetical judgment] I can . . . connect two false judgments with
one another, for there what matters is only the correctness of the connection “ the
form of the consequentia, on which the logical truth of these judgments rests.14

Note Kant says that antecedent and consequent can both be false: namely,
in asserting the hypothetical, we assert neither the antecedent nor the
consequent. We only assert that there is a relation of consequence
between them. So, they can both be false, or they can both be true. Or
perhaps even (as in our material conditional) the antecedent can be false
and the consequent true, without this putting into question the truth of
the Konsequenz. But the important difference between Kant™s hypothetical
judgment and our material conditional is that in the former, the meaning
of the connective is not fixed by its truth conditions, but on the contrary
the truth conditions are fixed by the meaning of the connective: because
the meaning of ˜˜if . . . then™™ in a hypothetical judgment is that there is a
relation of Konsequenz between antecedent and consequent, the hypothet-
ical judgment is true only if its antecedent is false, or if its antecedent and

Immanuel Kant, Jasche Logic, x25, AAix, pp. 105“6.

consequent are both true. And of course these are necessary, but not
sufficient conditions. For these conditions could be satisfied and there
still be no relation of Konsequenz at all between antecedent and conse-
quent. For instance: ˜˜If my mother is French, New York is in America™™; ˜˜If
the moon is square, I can fly™™; ˜˜If the moon is square, New York is in
America.™™ All three hypothetical judgments are false, because there is no
Konsequenz between antecedent and consequent.
Now, one may wonder, then, what Kant™s form of hypothetical judgment
has at all in common with what we would call a logical form. Answer: what
makes the Konsequenz a logical form is that it grounds the two forms of
inference: modus ponens, modus tollens. For because of the meaning of the
Konsequenz, whoever asserts the antecedent is thereby committed to assert-
ing the consequent (modus ponens); and whoever denies the consequent is
thereby committed to denying the antecedent (modus tollens). Note that
these two forms of inference are just those that the meaning of the material
conditional allows. But we see here the same asymmetry as in the determin-
ation of the truth of the propositions themselves: just as the truth of the
material conditional depends on the truth of antecedent and consequent,
similarly the modus tollens and modus ponens are just rules of separation
stemming from the truth conditions of the conditional: if the conditional
is true and its antecedent is true, then the consequent is true; if the condi-
tional is true and the consequent is false, then the antecedent is false. For
the hypothetical on the other hand, the form of inference is grounded not
in the truth conditions, but in the meaning of the Konsequenz. Nevertheless,
the forms of inference allowed are the same in both cases.
Consider now the propositions connected by the Konsequenz in a
hypothetical judgment. For Kant, the primary model for any judgment is
predication: A is B (subject“copula“predicate). Hypothetical judgments
themselves are to be understood as asserting a relation between predica-
tions. More specifically, according to Kant (who here too takes after Wolff )
what a hypothetical judgment asserts is that the predication expressed by
the consequent can be asserted only under the condition that the predica-
tion expressed in the antecedent be asserted. In the Jasche Logic, Kant writes:
There is an essential difference between the two propositions: all bodies
are divisible, and: if all bodies are composite, then they are divisible. In
the first proposition I assert the state of affairs [die Sache] directly; in the
second, I assert it only under a condition expressed problematically.15

Ibid., p. 106.

In the hypothetical judgment, the predication expressed by the conse-
quent is asserted only under the condition of the predication expressed by
the antecedent. This is why, again, in a hypothetical syllogism, the ante-
cedent being posited, the consequent should also be posited.
Kant says of hypothetical syllogisms that they are not really syllogisms,
because in them there is no middle term: one simply converts the ante-
cedent from a problematic to an assertoric proposition, and thus provides
the ground for asserting the consequent in the conclusion. As Kant explains:
A hypothetical syllogism is one that has a hypothetical proposition for its
major premise. It consists in two propositions: 1- an antecedent and 2- a
consequent, and it is achieved either through modus ponens or through
modus tollens.
Note: Hypothetical syllogisms thus have no middle term, but in them
the Konsequenz of a proposition from another proposition is shown. “
Namely, the major premise expresses the Konsequenz of two proposi-
tions, of which the first is a premise, the second is a conclusion. The
minor premise is a transformation of the problematic condition into a
categorical proposition.16

So, to take up Kant™s example of hypothetical judgment above, a
hypothetical syllogism formed from such a judgment would be: ˜˜If
bodies are composite, then they are divisible; bodies are composite; so,
they are divisible.™™ One might want to make explicit the fact that what is
asserted in the consequent is asserted of all bodies, together with the
Wolffian idea of an added condition, and write: ˜˜All bodies, if composite,
are divisible; all bodies are composite; so, all bodies are divisible.™™
But there can be more complex cases: cases that combine features of
categorical and hypothetical syllogisms. In a categorical syllogism, there
is a middle term by the mediation of which, in the conclusion, a parti-
cular class of objects is subsumed under the predicate of the major
premise. Now, consider the syllogism: ˜˜All stones, if lit by the sun, get
warm; the stones along the river are lit by the sun; therefore, they get
warm.™™ Such a syllogism combines features of a categorical (subsump-
tion of the subject of the minor premise under the subject, and thus
under the predicate, of the major premise) and of the hypothetical
(assertion in the minor premise of the antecedent of the major premise).
I suggest that when Kant talks of the ˜˜strict universality of a rule™™
contained in the concept of cause, what he has in mind is precisely this

Jasche Logic, x75, AAix, p. 129.

kind of mixed premise. And the ˜˜positing™™ of something that results in
the ˜˜positing™™ of something else similarly has the features of both the
categorical subsumption of an instance and the hypothetical assertion of
the antecedent. In other words, to think a causal connection between the
stone™s being lit by the sun and the stone™s becoming hot is to think that
the proposition ˜˜this stone is lit by the sun™™ being posited, the proposi-
tion ˜˜this stone is becoming hot™™ should be posited, which amounts to
thinking the first as an instantiation of the antecedent, the second as an
instantiation of the consequent, in the (implicit) strictly universal rule: all
stones, if lit by the sun, get warm. This is why Kant says that the concept
of cause (the sun™s being by its light the cause of the stone™s getting hot)
contains ˜˜the strict universality of the rule.™™
Three caveats: first of all, what we are talking about in a causal judg-
ment are empirical states of affairs. Kant™s question, like Hume™s, is how
a necessary connection can be thought to exist between two distinct
states of affairs which we know only empirically (matters of fact).
Second, the relation between antecedent and consequent has to be
synthetic: if asserting the predicate of the consequent follows analytically
from asserting the antecedent, then we do not have a causal connection.
˜˜All bodies, if composite, are divisible™™, is such an example. Third, if the
connection is itself an empirical generalization, we do not have a causal
connection. For instance, ˜˜All stones in this garden, if the sun shines on
them, are warm (I™ve checked).™™ This is not a causal connection.
To sum up, for the hypothetical to express a causal connection, it has to
be the case (1) that the states of affairs connected in the judgment are
empirical, (2) that the connection is synthetic, (3) that it has strict univer-
sality. Because only if I can presuppose a premise with strict universality
can I state, given one case (the sun shines of the stone) that this case being
posited, the consequent must be posited: the stone gets warm. In other
words, to think a causal connection between two states of affairs is to think
the one as the posited antecedent (in the minor premise) the other as the
posited consequent (in the conclusion) of a strictly universal rule.
In Kant™s terms, then, the difficulty inherent in the concept of cause
may be reduced to the following: how can a hypothetical judgment be
universally and necessarily true although it is not analytically true (its
consequent is not analytically contained in its antecedent)? When trying
to ground the ˜˜strict universality of the rule™™ contained in the concept of
cause, Kant is on the look-out for hypothetical judgments in which the
connection of antecedent and consequent is as strictly universal and
necessary as is the analytical connection of concepts or propositions; he

is looking for a way to move from the ˜˜positing™™ of the antecedent to the
˜˜positing™™ of its consequent by a modus ponens which is as rigorously
grounded as a modus ponens formed from an analytically true proposi-
tion, even though the connection contained in the supposed premise is
in fact synthetic, and its components are wholly empirical. To say that
there is a causal relation between the stone™s being lit by the sun and its
being warm is to say that the if . . . then connection between these two
states is as necessarily and universally true as the if . . . then connection
between perfect justice and the punishment of the wicked, although in
the case of the stone™s being lit and its getting warm I have only repeated
observation to vouch for my statement of an if . . . then connection.
The transition from a judgment which merely recounts repeated observ-
ation to a causal judgment (which amounts to claiming universal validity
and necessity for the rule: ˜˜If a stone is lit by the sun, then it gets warm™™) is
what Kant calls, in the Prolegomena, a transition from a mere ˜˜judgment of
perception™™ to a ˜˜judgment of experience.™™ A judgment of perception, he
says, holds only ˜˜for me, and in the present state of my perception.™™
A judgment of experience, if true, is true ˜˜for all, and at all times.™™ This
is because what it expresses is not just a repeated combination of per-
ceived events (I have repeatedly experienced that when the stone was lit
up by the sun, it became warm), but a connection in the objects themselves
such that if sun shines on the stone, the stone gets warm.17 But what
makes it possible to assert such a connection? What allows the transition
from the mere statement of a repeatedly observed occurrence (judgment
of perception) to a hypothetical judgment for which we claim the ˜˜strict
universality of a rule™™ (judgment of experience)? Kant™s response is that
we presuppose the necessary truth of another judgment, prior to both the
judgment of perception and the judgment of experience. We presuppose
the truth of a judgment that states that appearances, the objects of our
perception and experience, are ˜˜in themselves determined™™ with respect
to the logical form of our hypothetical judgment. We presuppose, in other
words, that appearances are in themselves, as empirical objects, connected

Cf. the striking manner in which Kant defines the role of the categories in Prolegomena
x21“a, AAiv, p. 304:
˜˜The judgment of experience must add to the sensible intuition and its logical connec-
tion in a judgment (according to which it has been made universal by comparison) some-
thing that determines the synthetic judgment as necessary and thereby as universal; and
this can be nothing other than the concept which represents the intuition as in itself
determined with respect to one form of judgment rather than another [my emphasis]: that is to
say, a concept of that synthetic unity of intuitions which can be represented by a given
logical function of judgment.™™

by a chain of causal connections, or we presuppose the universal validity of
the causal principle. Because we make such a presupposition, we allow
ourselves, upon repeated observation of similar events, to move from
such repeated observation to a causal judgment (a hypothetical for
which we claim the ˜˜strict universality of a rule™™).
What justified such a presupposition? For an answer to this question,
in the Prolegomena Kant merely refers us to the Critique of Pure Reason.18
Before we consider this answer, we can already note that the structure of
Kant™s response to ˜˜Hume™s problem™™ turns out to be the exact reverse
of Hume™s own. Hume derived the universal principle from the parti-
cular cases of causal connections and the particular cases of causal con-
nection from repeated successions of similar events. Kant says that we
derive a causal connection from any given repetition of similar events
because we already have the universal causal principle.
What we need from the Critique, then, are answers to three main
questions. First, is it the case that we presuppose the truth of the causal
principle? Second, supposing we do presuppose its truth, is it indeed
true, i.e. do we have the right to presuppose its truth? (This is, in effect,
the quid juris question of the Critique: by what right do we make use, in

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