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neither follows nor precedes that of the determining.4

Kant gives two examples. Here is the first: we have a consequently
determining reason for affirming that the world contains many ills,
namely our own experience of those ills. But if we also look for an
antecedently determining reason, we must search for that which, in
the essence of the world, or in its relation to some other being, provides
the ground or reason for the predicate™s (for example, ˜˜containing many
ills™™) being attributed to the subject (˜˜world™™) and its opposite (say:
˜˜perfectly good™™) being excluded.
Kant™s second example is the following: we have a consequently
determining reason for asserting that light travels not instantaneously
but with an ascribable speed. This reason consists in the eclipses of the
satellites of Jupiter “ or more precisely, in the delay in our observation of
those eclipses “ a delay that is a consequence of the non-instantaneous
travel of light. But we also have an antecedently determining reason.
This consists, according to Kant, in the elasticity of the aether particles
through which light travels, which delays its movement.5

New Elucidation, x2, AAii, p. 391.
Kant™s view of light as a movement of fine aether particles is borrowed from Descartes. But
Kant opposes Descartes in maintaining that these particles are elastic rather than absolutely
hard, thus delaying the transmission of light (see Kant, New Elucidation, AAii, pp. 391“2,
and Rene Descartes, Principes de la philosophie, ed. Charles Adam, Paul Tannery, and Centre
National de la Recherche Scientifique, 12 vols. (Paris: Librairie philosophique Vrin, 1971),
part iii, xx63“4 and part iv, x28, vol. ix-2, pp. 135“6 and 215; trans. John Cottingham,

The distinction between antecedently and consequently determining
reason, as presented here, is disconcerting: clearly, the two kinds of
reason are quite heterogeneous. One is a reason for holding the propo-
sition to be true. The other is a reason for the proposition™s being true,
that is, for the state of affairs™ obtaining. Kant does recognize this differ-
ence, since at the end of his definition he characterizes the former as a
reason for knowing (ratio cognoscendi), the latter as a reason for being or
coming to be (ratio essendi vel fiendi). But he does not stress this aspect of
the distinction in his initial characterization of reasons. Both reasons are
described as reasons for the determination of a subject with respect to a
predicate. This seeming hesitation in Kant™s definition of reason
(ground) will be important for what follows.
Having thus defined the notion of reason (ratio) and distinguished two
main kinds of determining reason, Kant criticizes Wolff™s definition.
Wolff, he says, ˜˜defines reason (or ground) as that from which it is
possible to understand why something is rather than is not [definit enim
rationem per id, unde intelligi potest, cur aliquid potius sit, quam non sit].™™6 Kant
objects that this definition is circular. It amounts to saying: ˜˜Reason is
that from which it is possible to understand for what reason something is
rather than is not.™™ This circularity is avoided if one says, rather: reason
is that by which the subject of a proposition is determined, that is, that by
virtue of which a predicate is posited and its opposite is negated. That is
why it is preferable to speak of determining rather than sufficient
But is it so clear that the Wolffian definition is circular? It is so only if
the same thing is meant by ˜˜reason™™ (in: ˜˜reason is that from which it is
possible to understand,™™ ratio est, unde intelligi potest) and by ˜˜why™™ (˜˜why
something is rather than is not,™™ cur aliquid sit potius quam non sit). But that
is not necessarily so. Wolff might have meant that the reason in the
proposition is that from which it is possible to understand the why (the
reason) in things. The parallelism of logical and ontological relations
Robert Stoothof, and Dugald Murdoch, Principles of Philosophy, in The Philosophical Writings
of Descartes, 3 vols. (Cambridge: Cambridge University Press, 1984, 1985, 1991), i , pp. 260,
270. I am grateful to Michelle and Jean-Marie Beyssade for having clarified the Cartesian
example for me.
Cf. Christian Wolff, Philosophia Prima sive Ontologia (Frankfurt-am-Main and Leipzig, 1736;
repr. in Gesammelte Werke (Hildesheim and New York: Georg Olms, 1962“), x56. Kant
slightly alters Wolff™s definition. Wolff actually writes, ˜˜Per rationem sufficientem intelligi-
mus id, unde intelligitur, cur aliquid sit.™™ ˜˜By sufficient reason, we understand that from
which it is understood why something is.™™ As Kant™s main discussion is about the meaning of
cur (why), however, the variation is of no consequence and we can ignore it.
New Elucidation, AAi, p. 393.

would justify Wolff™s statement and dissolve the objection of circularity.
The reason Kant nevertheless formulates this objection is probably that
he shares Wolff™s view that understanding the reason in propositions
and the reason in things is really understanding one and the same thing,
the same object of intellect. But what we want to know is what is thereby
understood. Response: what is understood is what determines a subject
in relation to a predicate, that is to say, what posits the predicate and
excludes its negation.
This is where the distinction between antecedently and consequently
determining reason comes into play. But if one accepts it, then another,
more severe objection to Wolff is in order. For as we saw, Kant expressly
says that the antecedently determining reason is a reason why (ratio cur)
but that the consequently determining reason is only a reason that (ratio
quod). Given this distinction, why does Kant not make this objection to
Wolff (the reason why is not the only kind of reason), an objection that
seems, at this point, more damning than that of circularity?
This is probably because he also shares Wolff™s (and Leibniz™s) view
that the only reason worthy of the name is the antecedently determining
reason. For it is not only just a reason for our holding a proposition to be
true, but a reason for its being true. Here™s what he says on the example
of the world and its ills:
Suppose we look for the reason of ills in the world. We have thus a
proposition: the world contains many ills. We are not looking for the
reason that or reason of knowing, for our own experience plays this role;
but we are looking for the reason why or the reason for coming to be [ratio
cur scilicet fiendi], i.e. a reason such that when it is posited, we understand
that the world is not undetermined with respect to the predicate but on
the contrary, the predicate of ills is posited, and the opposite is excluded.
The reason (ground), therefore, determines what is at first indeterminate.
And since all truth is produced by the determination of a predicate in a subject, the
determining reason is not only a criterion of truth, but its source, without which
there would remain many possibles, but nothing true).8

The whole ambiguity of Kant™s position is manifest in this passage. For
on the one hand, Kant™s notion of reason (ground) is characterized as a
reason for asserting a predicate of a subject, without which there would
be no proposition susceptible of truth or falsity, that is to say, on our part,
us judging subjects, no act of asserting rather than suspending our

Ibid., p. 392. Emphasis in the last sentence is mine.

judgment. And the force of his statement that there must always be a
reason for determining a subject with respect to a predicate clearly rests
on the common intuition that we need a reason for holding a proposition
to be true. But understood in this way, the reason could very well be
what Kant calls a mere criterion of truth and not its source. Nonetheless,
Kant immediately adds: the reason is not simply a criterion. To deserve
the name ˜˜reason,™™ it has to be the source of the truth of the proposition.
The very same ambiguity is at work in Kant™s pre-critical proof of the
principle of sufficient reason (or of determining reason). The principle is
thus formulated: ˜˜Nothing is true without a determining reason.™™ Here,
˜˜nothing™™ clearly means ˜˜no proposition,™™ as is shown in the proof that
immediately follows Kant™s statement of the principle:
1 All true propositions state that a subject is determined with respect to a
predicate, that is to say, that this predicate is affirmed and its opposite
is excluded.
2 But a predicate is excluded only if there is another notion that, by the
principle of contradiction, precludes its being affirmed.
3 In every truth there is therefore something that, by excluding the
opposite predicate, determines the truth of the proposition (from [1]
and [2]).
4 That is precisely what is called the determining reason (definition).
5 So, nothing is true without a determining reason (from [3] and [4]).9
This ˜˜proof™™ does little more than restate what was already said in
Kant™s initial characterization of a reason: a true proposition is one in
which a subject is determined with respect to a predicate (premise [1]).
What does the determination is the reason (premise [2], and proposi-
tions [3] and [5] derived from [1] and [2]).
Consider again the proposition: ˜˜Light travels with an assignable,
finite speed.™™ To think that the proposition is true is to assert that the
predicate, ˜˜travels with an assignable, finite speed,™™ belongs to the sub-
ject, ˜˜light,™™ and that its negation, ˜˜travels instantaneously,™™ is excluded
(this is what premise [1] says). However, for such an exclusion to obtain,
there needs to be a reason (otherwise we might admit as problematic or
as possible both judgments, light travels instantaneously, light travels
with an assignable, finite speed). Now, the consequently determining
reason provided by the delay in our observation of the eclipses of

Ibid., prop. 5, AAi, p. 393. I have followed the progress of Kant™s argument, only ignoring a
few repetitions.

Jupiter™s satellites excludes that the travel should be instantaneous, by
virtue of the syllogism in modus tollens: ˜˜If all light-travel is instantaneous,
there is no delay in the eclipses of Jupiter™s satellites; however, there is a
delay. So, it is not the case that all light-travel is instantaneous.™™ For its
part the antecedently determining reason excludes instantaneous travel
by the syllogism in modus ponens: ˜˜If aether particles are elastic, then all
light travel is delayed (non-instantaneous); however, aether particles are
elastic. So, all light travel is delayed.™™ The exclusion of the opposite
predicate may be derived either from the modus tollens appropriate to
the consequently determining reason or from the modus ponens appro-
priate to the antecedently determining reason.10
We see again in this example that, even if it is granted that a reason is
needed for moving from a merely problematic judgment (one with
respect to which assent is suspended) to a proposition (a judgment
asserted as true), it does not follow at all that for every truth there is an
antecedently determining reason, ratio cur. Nonetheless, just as in his
definition of reason or ground (ratio, Grund) Kant moved without any
argument from distinguishing between two types of reason (antece-
dently and consequently determining reason) to maintaining that only
one kind of reason is relevant (the antecedently determining reason,
reason for being or becoming, reason why), similarly here, Kant sub-
stitutes for the cautious conclusion that it is in the nature of propositions
(assertoric judgments) that there should be a reason for the determin-
ation of the subject in relation to the predicate (whether this reason be

A few quick remarks regarding my presentation of the two kinds of reasons in terms of
modus ponens and modus tollens: Kant does not explicitly give such an explanation. But the
expressions ratio consequenter determinans and ratio antecedenter determinans seem to me to be
an unambiguous reference to the idea of determining by the antecedent and determining
by the consequent of a hypothetical judgment. The corresponding logical forms are modus
ponens and modus tollens. Making this reference explicit has three main advantages. (1) We
see more clearly that the two species of ratio do not have the same force. The ratio ponens
allows us to assert universally that all light-travel is delayed (it allows us to exclude in all
cases that light-travel is instantaneous). The ratio tollens only allows us to deny a universal
judgment, excluding in this case that light-travel is instantaneous and thus allows us to
deny the universal judgment: all light-travel is instantaneous. (2) We shall see in a moment
that when Kant, just a few years later, puts into doubt the universal validity of the
antecedently determining reason, he expresses this doubt in terms of ratio ponens: he
asks, what is the synthetic ratio ponens? This confirms that his notion of reason or ground
had always been thought in light of modus ponens (or tollens). (3) In the critical period, when
Kant distinguishes a logical principle and a transcendental principle of sufficient reason,
he will define the logical principle in terms that clearly refer to the two forms, modus ponens
and modus tollens. There is thus a deep continuity in his thought on this point, which it is
important to keep in mind (see below, pp. 137“8).

antecedently or consequently determining), a far more ambitious state-
ment: there is always an antecedently determining reason for any truth:
That the knowledge of truth always demands that we perceive a reason,
this is affirmed by the common sense of all mortals. But most often we
are content with a consequently determining reason, when what is at
issue is only our certainty; but it is easy to see, from the theorem and the
definition, that there is always an antecedently determining reason or, if
you prefer, a genetic or an identical reason; for the consequently deter-
mining reason does not make truth, but only presents it.11

From this ambitious version of the principle of sufficient reason Kant
derives important metaphysical consequences that in the years to come
will motivate his growing discomfort with his own pre-critical position,
and more generally with rational metaphysics.
The first consequence of this is a proof of the principle of sufficient
reason for the existence of contingent things. This is where the concept
of cause occurs for the first time in the New Elucidation: the reason of
existence is a cause.
As a preliminary to proving a principle of sufficient reason of exis-
tence, Kant first establishes the negative proposition, ˜˜It is absurd that
something should have in itself the reason of its existence.™™12 Kant™s
proof for this proposition rests on the “ unquestioned “ assumption
that a cause necessarily precedes its effect in time. So, if a thing were
the cause of itself, it would have to precede its own existence in time,
which is absurd. Therefore nothing is the reason of its own existence:
Kant expressly opposes Spinoza™s notion of a God that is causa sui, cause
of itself.
On the other hand it is true to say that God™s existence is necessary, or
that the proposition, ˜˜God exists,™™ is necessarily true. But this is not
because God is the cause of himself. It is not even because his existence
is contained in his essence (as in the ˜˜Cartesian proof™™). Rather, it is
because he is the unique being that is the ground of everything possible.
I will not attempt to lay out and analyze Kant™s proof of this point. Let me
just note that, according to Kant™s pre-critical view, if we affirm the
existence of God, or if we assert the proposition, ˜˜God exists,™™ as
necessarily true, it is not by virtue of an antecedently determining
reason (whether of being, of coming to be, or of existing). There is no

New Elucidation, prop. 5, AAi, p. 394.

antecedently determining reason for God™s existence, not even in God
himself. But we have a reason to assert that he exists and that this
existence is absolutely necessary. We know this by a reason for knowing
of a unique kind, which Kant will further elaborate in the 1763 text, The
Only Possible Argument in Support of a Demonstration of the Existence of God
and then thoroughly refute in the Transcendental Ideal of the first
Kant then sets about proving a principle of antecedently determining
reason for the existence of contingent things. The principle is: ˜˜Nothing
contingent can be without an antecedently determining reason (a cause)
of its existence.™™
The proof, roughly summarized, is the following:
1 Suppose a contingent thing exists without an antecedently determin-
ing reason.
2 As an existing thing, it is completely determined, and the opposite of
each of its determinations is excluded (definition of existence as com-
plete determination).
3 But according to the hypothesis, this exclusion has no other reason
than the thing™s existence itself. Even more, this exclusion is identical:
the very fact that the thing exists is what excludes its non-existing.
4 But this amounts to saying that its existence is absolutely necessary,
which is contrary to the hypothesis.
5 So, nothing contingent can be without an antecedently determining

Ibid., p. 395. The Only Possible Argument in Support of a Demonstration of the Existence of
God, AAii, pp. 83“4, trans. in Theoretical Philosophy, 1755“1770. Critique of Pure Reason,
A581“2/B609“10. The pre-critical proof rests on the idea that the notion of possible has a
˜˜formal™™ aspect (what is possible is what is thinkable, and what is thinkable is what is non-
contradictory) and a ˜˜real™™ aspect (something must be thought). Both aspects presuppose
that what is possible (thinkable) is grounded in one and the same being, which thus
necessarily exists. The Transcendental Ideal will oppose to this ˜˜proof™™ that the matter
of all possibilities, as well as the comparability of all possibilities (the formal aspect of the
possible) are provided not by an absolutely necessary being, but by the whole of reality,
given to the senses, presupposed for the collective unity of possible experience and of its
objects (see A581“2/B609“10, and ch. 8 in this volume, pp. 214“23). Gerard Lebrun has
convincingly shown that already in the pre-critical period, by renouncing the Cartesian
ontological proof Kant has given up the metaphysical notion of essence as a degree of
perfection and initiated instead a consideration of the conditions under which thoughts
´ ´
have meaning. See Gerard Lebrun, Kant et la fin de la metaphysique (Paris: Armand Colin,
1970), pp. 13“34. See also KCJ, p. 154.

The proof rests on three presuppositions: (a) existence is complete
determination: an existing thing is individuated by the fact that, given
the totality of possible predicates, for each and every one of them, either
it or its negation is true of the individual existing thing; (b) as such, it falls
under the principle of determining reason stated above; (c) this princi-
ple should be understood as a principle of antecedently determining
reason. If we accept all three presuppositions, then we can avoid the
absurd conclusion that a contingent existence is absolutely necessary
only if we accept that every contingent thing has an antecedently deter-
mining reason not only of its determinations (ratio essendi vel fiendi) but of
its existence itself (ratio existendi).
The second consequence of the ambitious version of the principle of
sufficient reason is a ˜˜principle of succession,™™ stated as follows: ˜˜No
change can affect substances except insofar as they are related to other
substances, and their reciprocal dependence determines their mutual
change of state.™™ Kant™s argument for this principle is that if the ground
or reason of the change of states of a substance were within it, then the
state that comes to be should always have been (given that its ratio fiendi
was always present in the substance). So, a state that was not and comes to
be must have its ground not in the substance itself but in its relation to
another substance or to other substances. (Note that this is a fundamen-
tally anti-Leibnizian view: contrary to Leibniz, according to Kant indivi-
dual substances have real influence upon one another™s states.)14
Finally, Kant devotes a fairly long discussion to the relation between
the principle of sufficient reason and human freedom. Here he opposes
a view defended by his predecessor Crusius. According to Crusius, in
some cases the existence of a state of affairs or an event is without an
antecedently determining reason. It can be affirmed only by virtue of
a ratio cognoscendi, which is none other than the existence of the state
of affairs itself as attested by experience. Such is the case with free
action: that the will should decide of its own free choice, without any

This principle is complemented by a ˜˜principle of coexistence™™: ˜˜Finite substances stand in
no relation to one another through their mere existence and have no community except
insofar as they are maintained in reciprocal relations through the common principle of
their existence, namely the divine intellect™™ (New Elucidation, AAi, pp. 412“13). Just as the
˜˜principle of succession™™ is the ancestor of the Second Analogy of Experience, the ˜˜prin-
ciple of coexistence™™ is the ancestor of the Third Analogy. But of course, in the Critique of
Pure Reason, as we shall see, Kant will prove both principles from the conditions of our
experience of objective time-determinations, not from the application of a previously
established principle of sufficient reason. Undertaking a detailed analysis of those two
principles and their proof in the New Elucidation is beyond the scope of the present chapter.

antecedently determining reason, in favor of one action rather than
another, is a fact attested by experience.15 To this Kant objects that if
an action, or the will™s determination to act, were without an antece-
dently determining reason then, since the determination of the will to act
and the ensuing action have not always existed, their transition into
existence would remain undetermined “ that is to say, for the action as
well as for the determination of the will, it would remain undetermined
that it should be rather than not be. Kant™s response in this case rests on
the same presuppositions as his general argument concerning the rea-
son of existence: in order to justifiably assert that a thing has come to be,
we need not only a ratio cognoscendi (ratio consequenter determinans), but
also a ratio fiendi, the ratio antecedenter determinans of its complete
To the question: ˜˜is this principle of reason applied to human action
compatible with freedom of the will and freedom of action?™™ Kant
answers “ again against Crusius “ that being free is not acting without a
reason, but on the contrary acting from an internal reason that inclines
one to act without any hesitation or doubt in one way rather than
another. Kant, here, is faithfully Leibnizian.
I have suggested above that the main weakness of Kant™s argument is
the way in which he jumps from the distinction between antecedently
and consequently determining reason for asserting the truth of a pro-
position to the claim that there is always an antecedently determining
reason, a reason why. It will not be long before the universality of the
ratio cur raises doubts in Kant™s mind. But his doubts will focus at first not
on the principle of reason and its proof, but on particular cases of
connection between the ratio and the rationatum. For the analysis of
these cases, Kant introduces, at the beginning of the 1760s, the distinc-
tion between logical reason and real reason (or logical ground and real
ground), and emphasizes the synthetic character of the real ground.
When the Humean alarm clock does its work, the investigation of the
relationship of real ground to its consequences becomes generalized into
an investigation concerning the notion of reason or ground in general,
and the principle of sufficient reason itself.

Cf. Crusius, Dissertatio de usu et limitibus principii rationis determinantis, vulgo sufficientis
(Leipzig, 1743) (Dissertation on the use and limits of the principle of determining reason, commonly
known as the principle of sufficient reason). See also Entwurf der notwendigen Vernunftwahrheiten,
wie sie den zufaligen entgegen gesetzt werden (Metaphysik), 2nd edn (Leipzig, 1753) (Outline of the
necessary truths of reason, insofar as they are opposed to contingent truths (Metaphysics)), esp. x126.
New Elucidation, props. 8 and 9, AAi, pp. 396“7, 398“406.

Skeptical interlude: logical reason and real reason.
The synthetic ratio ponens
In the Lectures on Metaphysics from the 1760s, Kant remarks on the
difficulty of accounting for the relation between ratio and rationatum in
the case of what he now calls ratio realis (real ground), so as to distinguish
it from ratio logica (logical ground). The logical ground (or reason), he
says, is posited by identity. But the real ground is posited without
identity. The examples show that by ˜˜real ground™™ he means the relation
of ground that connects one existence to another existence, in other words
what, in the New Elucidation, he called ratio existendi, or cause:17

All grounds (reasons) are either logical, by which the consequence is
posited by the rule of identity, where the consequence is identical with

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