Im m anuel K ant’s Critique of
Practical Reason
(Com plete Notes)
Pr eface & Intr odu ction
Sum m ar y
Kant sketches out here what is to follow. Most of these two chapters focuses on
comparing the situation of theoretical and of practical reason and therefore discusses
how Critique of Practical Reason compares to Critique of Pure Reason.
Critique of Pure Reason was a critique of the pretensions of pure theoretical reason to
attain metaphysical truths beyond the ken of applied theoretical reason. Its conclusion
was that pure theoretical reason must be restrained, because it produces confused
arguments when applied outside its sphere. However, the Critique of Practical
Reason is not a critique of pure practical reason, but rather a defense of it as being
capable of grounding behavior superior to that grounded by desire-based practical
reasoning. It is a critique, then, of applied practical reason's pretensions. Pure practical
reason must be restrained but rather cultivated.
Kant tells us that while Critique of Pure Reason presented God, freedom, and
immortality as unknowable, the second Critique will mitigate that claim. Freedom is
knowable because it is revealed through the force of the moral law. God and immortality
are not, but now (practical) reason requires belief in them. One might still be
dissatisfied, wanting, say, proof of God's existence. Kant here invites his dissatisfied
opponent to actually provide such a proof, believing that none is forthcoming. The
discussion of freedom Kant holds to be especially important, for empiricists insist on
thinking of it as a purely psychological thing in the phenomenal world, a complete
confusion according to Kant.
Critique of Practical Reason can stand alone from the earlier Groundwork for a
Metaphysics of Morals, although it addresses some criticisms leveled against that work.
In particular, Kant will address the issue of why he did not first discuss the highest good
and then define the moral law in terms of it. A complete classification of duties will not
occur in the second Critique because such a classification depends on how people
contingently are. This work will proceed on a higher level of abstraction.
,While valid criticisms against the Groundwork of the Metaphysics of Morals are to be
addressed, Kant excoriates those criticisms he does not find helpful. He suggests that
some of the gaps reviewers find in his arguments are in fact only in their brains, which
are too lazy to grasp his ethical system as a whole. As for those who charge him with
writing incomprehensible jargon, he challenges them to find more suitable language for
his ideas, or otherwise to prove that they really are meaningless. Fortunately, Kant
reassures us, that while the speculations of the first Critique required language very
unlike common speech, this will be less true in the second Critique.
Finally, the sketch of Critique of Practical Reason is presented in the Introduction. It is
modeled on the first Critique. First, the Analytic will investigate the operations of the
faculty in question. Next, the Dialectic will investigate how it can go astray. Finally, the
Doctrine of Method follows, which will only be loosely analogous to its corresponding
first Critique section, discussing how to bring about psychological influence of pure
practical reason.
An alysis
Kant's comparison of Critique of Pure Reason and the Critique of Practical Reason in
the preface and his subsequent discussion in the introduction bring out one aspect of
Kant's writing: a tendency to model his works after one another. Here it is questionable
whether the structure of the Critique of Pure Reason was really so suitable for this book,
and whether the parallels he discusses are more illuminating or more
distracting. Critique of Pure Reason utilizes theoretical reasoning—roughly,
philosophical thinking—to examine the limits of the potential achievements of such
thinking. Critique of Practical Reason, however, as Kant points out, does not use pure
practical reason—decision-making based on reason and not on desire—to point out the
limitations of such decision- making. For one thing, it is unclear how one could "apply"
a faculty of decision-making in a book, which is better seen as a recording of theoretical
reason's activity.
Mainly though, Kant is not critiquing pure practical reason but lauding it, saying that it
is possible and that it is the ground of morality. True, we can say that he is thereby
attacking impure practical reason. Kant believes that although his beliefs about pure
practical reason are commonsensical, insofar as common sense can grasp them,
philosophers are liable to go astray and enshrine the self-serving calculations of impure
practical reason in the place of pure practical reason. But it remains to be seen whether
anything is really gained by setting up the analogy in the first place.
A point about the comparison which is important to remember is that the Critique of
Practical Reason does not simply contrast with the Critique of Pure Reason, in that it
critiques the impure reason which the first Critique still left unexamined. Rather, the
title of the first Critique is meant to be understood as elliptical for "The Critique of Pure
, Theoretical Reason," while the title of the second Critique can be understood as elliptical
for "The Critique of Impure Practical Reason." The pure/impure distinction, which has
to do with whether contingent, sensory factors are involved, is not the same as the
theoretical/practical distinction, which has to do with the faculty of knowing versus the
faculty of acting.
This work contains three sections: the Analytic, the Dialectic, and the Doctrine of
Method. The Analytic presents, in both critiques, the operations of the faculty in
question. In the case of the second Critique, this will turn out to be a derivation of the
one principle of pure practical reason, the categorical imperative, and an argument that
obeying it is equivalent to freedom. The Dialectic presents, in both Critiques, arguments
that the faculty in question can go astray. In the case of the second Critique, this will be
an argument that pure practical reason goes wrong when it seeks perfection
in this world, as well as an argument that what we should instead do is seek perfection
in the next world with God's help, making the assumption that immortality and God
exist. The Doctrine of Method in the first Critique plans out the future sciences of pure
theoretical reason; the Doctrine of Method in the second Critique plans out the future of
educating people in the use of pure practical reason.
We are also set up for Kant's 1797 "follow-up," the Metaphysics of Morals. The Critique
of Practical Reason contains the one true ultimate moral principle, the categorical
imperative. However, there is no full discussion of its application. That is because Kant
intends everything in the Critique of Pure Reason to proceed a priori, without any
reference to what, as a matter of contingent fact, human nature happens to be like.
Without such a theory, we cannot say what, concretely, our duties are. The role of
the Metaphysics of Morals is to give such a theory.
An alytic: Chapter On e
Sum m ar y
Practical reason is the faculty for determining the will, which operates by applying a
general principle of action to one's particular situation. A principle is either a mere
maxim if it is based on the agent's desires or a law if it holds universally. A principle that
presupposes a previous desire for some object in the agent always presupposes that the
agent happens to be the sort of person who cares for that sort of thing. But what the
agent is interested in is contingent, and so that principle is no law.
Suppose this is right. Then what can the practical law possibly be? If I say that the law is
to serve God, the principle can be attacked on its dependence on interest in God, if I say
that the law is to seek the greatest good, the principle can be attacked on its dependence
on interest in the greatest good, etc. The answer is that the source of the law-likeness of
Practical Reason
(Com plete Notes)
Pr eface & Intr odu ction
Sum m ar y
Kant sketches out here what is to follow. Most of these two chapters focuses on
comparing the situation of theoretical and of practical reason and therefore discusses
how Critique of Practical Reason compares to Critique of Pure Reason.
Critique of Pure Reason was a critique of the pretensions of pure theoretical reason to
attain metaphysical truths beyond the ken of applied theoretical reason. Its conclusion
was that pure theoretical reason must be restrained, because it produces confused
arguments when applied outside its sphere. However, the Critique of Practical
Reason is not a critique of pure practical reason, but rather a defense of it as being
capable of grounding behavior superior to that grounded by desire-based practical
reasoning. It is a critique, then, of applied practical reason's pretensions. Pure practical
reason must be restrained but rather cultivated.
Kant tells us that while Critique of Pure Reason presented God, freedom, and
immortality as unknowable, the second Critique will mitigate that claim. Freedom is
knowable because it is revealed through the force of the moral law. God and immortality
are not, but now (practical) reason requires belief in them. One might still be
dissatisfied, wanting, say, proof of God's existence. Kant here invites his dissatisfied
opponent to actually provide such a proof, believing that none is forthcoming. The
discussion of freedom Kant holds to be especially important, for empiricists insist on
thinking of it as a purely psychological thing in the phenomenal world, a complete
confusion according to Kant.
Critique of Practical Reason can stand alone from the earlier Groundwork for a
Metaphysics of Morals, although it addresses some criticisms leveled against that work.
In particular, Kant will address the issue of why he did not first discuss the highest good
and then define the moral law in terms of it. A complete classification of duties will not
occur in the second Critique because such a classification depends on how people
contingently are. This work will proceed on a higher level of abstraction.
,While valid criticisms against the Groundwork of the Metaphysics of Morals are to be
addressed, Kant excoriates those criticisms he does not find helpful. He suggests that
some of the gaps reviewers find in his arguments are in fact only in their brains, which
are too lazy to grasp his ethical system as a whole. As for those who charge him with
writing incomprehensible jargon, he challenges them to find more suitable language for
his ideas, or otherwise to prove that they really are meaningless. Fortunately, Kant
reassures us, that while the speculations of the first Critique required language very
unlike common speech, this will be less true in the second Critique.
Finally, the sketch of Critique of Practical Reason is presented in the Introduction. It is
modeled on the first Critique. First, the Analytic will investigate the operations of the
faculty in question. Next, the Dialectic will investigate how it can go astray. Finally, the
Doctrine of Method follows, which will only be loosely analogous to its corresponding
first Critique section, discussing how to bring about psychological influence of pure
practical reason.
An alysis
Kant's comparison of Critique of Pure Reason and the Critique of Practical Reason in
the preface and his subsequent discussion in the introduction bring out one aspect of
Kant's writing: a tendency to model his works after one another. Here it is questionable
whether the structure of the Critique of Pure Reason was really so suitable for this book,
and whether the parallels he discusses are more illuminating or more
distracting. Critique of Pure Reason utilizes theoretical reasoning—roughly,
philosophical thinking—to examine the limits of the potential achievements of such
thinking. Critique of Practical Reason, however, as Kant points out, does not use pure
practical reason—decision-making based on reason and not on desire—to point out the
limitations of such decision- making. For one thing, it is unclear how one could "apply"
a faculty of decision-making in a book, which is better seen as a recording of theoretical
reason's activity.
Mainly though, Kant is not critiquing pure practical reason but lauding it, saying that it
is possible and that it is the ground of morality. True, we can say that he is thereby
attacking impure practical reason. Kant believes that although his beliefs about pure
practical reason are commonsensical, insofar as common sense can grasp them,
philosophers are liable to go astray and enshrine the self-serving calculations of impure
practical reason in the place of pure practical reason. But it remains to be seen whether
anything is really gained by setting up the analogy in the first place.
A point about the comparison which is important to remember is that the Critique of
Practical Reason does not simply contrast with the Critique of Pure Reason, in that it
critiques the impure reason which the first Critique still left unexamined. Rather, the
title of the first Critique is meant to be understood as elliptical for "The Critique of Pure
, Theoretical Reason," while the title of the second Critique can be understood as elliptical
for "The Critique of Impure Practical Reason." The pure/impure distinction, which has
to do with whether contingent, sensory factors are involved, is not the same as the
theoretical/practical distinction, which has to do with the faculty of knowing versus the
faculty of acting.
This work contains three sections: the Analytic, the Dialectic, and the Doctrine of
Method. The Analytic presents, in both critiques, the operations of the faculty in
question. In the case of the second Critique, this will turn out to be a derivation of the
one principle of pure practical reason, the categorical imperative, and an argument that
obeying it is equivalent to freedom. The Dialectic presents, in both Critiques, arguments
that the faculty in question can go astray. In the case of the second Critique, this will be
an argument that pure practical reason goes wrong when it seeks perfection
in this world, as well as an argument that what we should instead do is seek perfection
in the next world with God's help, making the assumption that immortality and God
exist. The Doctrine of Method in the first Critique plans out the future sciences of pure
theoretical reason; the Doctrine of Method in the second Critique plans out the future of
educating people in the use of pure practical reason.
We are also set up for Kant's 1797 "follow-up," the Metaphysics of Morals. The Critique
of Practical Reason contains the one true ultimate moral principle, the categorical
imperative. However, there is no full discussion of its application. That is because Kant
intends everything in the Critique of Pure Reason to proceed a priori, without any
reference to what, as a matter of contingent fact, human nature happens to be like.
Without such a theory, we cannot say what, concretely, our duties are. The role of
the Metaphysics of Morals is to give such a theory.
An alytic: Chapter On e
Sum m ar y
Practical reason is the faculty for determining the will, which operates by applying a
general principle of action to one's particular situation. A principle is either a mere
maxim if it is based on the agent's desires or a law if it holds universally. A principle that
presupposes a previous desire for some object in the agent always presupposes that the
agent happens to be the sort of person who cares for that sort of thing. But what the
agent is interested in is contingent, and so that principle is no law.
Suppose this is right. Then what can the practical law possibly be? If I say that the law is
to serve God, the principle can be attacked on its dependence on interest in God, if I say
that the law is to seek the greatest good, the principle can be attacked on its dependence
on interest in the greatest good, etc. The answer is that the source of the law-likeness of
