cannot be given according to the laws of the world of sense；
although the practical consequences of the idea belong to the world of
sense； namely； the actions that aim at realizing the summum bonum；
we will therefore endeavour to set forth the grounds of that
possibility； first； in respect of what is immediately in our power；
and then； secondly； in that which is not in our power； but which
reason presents to us as the supplement of our impotence； for the
realization of the summum bonum （which by practical principles is
necessary）。
III。 Of the Primacy of Pure Practical Reason in its
Union with the Speculative Reason。
By primacy between two or more things connected by reason； I
understand the prerogative； belonging to one； of being the first
determining principle in the connection with all the rest。 In a
narrower practical sense it means the prerogative of the interest of
one in so far as the interest of the other is subordinated to it；
while it is not postponed to any other。 To every faculty of the mind
we can attribute an interest； that is； a principle； that contains
the condition on which alone the former is called into exercise。
Reason； as the faculty of principles； determines the interest of all
the powers of the mind and is determined by its own。 The interest of
its speculative employment consists in the cognition of the object
pushed to the highest a priori principles： that of its practical
employment； in the determination of the will in respect of the final
and plete end。 As to what is necessary for the possibility of any
employment of reason at all； namely； that its principles and
affirmations should not contradict one another； this constitutes no
part of its interest； but is the condition of having reason at all； it
is only its development； not mere consistency with itself； that is
reckoned as its interest。
If practical reason could not assume or think as given anything
further than what speculative reason of itself could offer it from its
own insight； the latter would have the primacy。 But supposing that
it had of itself original a priori principles with which certain
theoretical positions were inseparably connected； while these were
withdrawn from any possible insight of speculative reason （which；
however； they must not contradict）； then the question is： Which
interest is the superior （not which must give way； for they are not
necessarily conflicting）； whether speculative reason； which knows
nothing of all that the practical offers for its acceptance； should
take up these propositions and （although they transcend it） try to
unite them with its own concepts as a foreign possession handed over
to it； or whether it is justified in obstinately following its own
separate interest and； according to the canonic of Epicurus； rejecting
as vain subtlety everything that cannot accredit its objective reality
by manifest examples to be shown in experience； even though it
should be never so much interwoven with the interest of the
practical （pure） use of reason； and in itself not contradictory to the
theoretical； merely because it infringes on the interest of the
speculative reason to this extent； that it removes the bounds which
this latter had set to itself； and gives it up to every nonsense or
delusion of imagination？
In fact； so far as practical reason is taken as dependent on
pathological conditions； that is； as merely regulating the
inclinations under the sensible principle of happiness； we could not
require speculative reason to take its principles from such a
source。 Mohammed's paradise； or the absorption into the Deity of the
theosophists and mystics would press their monstrosities on the reason
according to the taste of each； and one might as well have no reason
as surrender it in such fashion to all sorts of dreams。 But if pure
reason of itself can be practical and is actually so； as the
consciousness of the moral law proves； then it is still only one and
the same reason which； whether in a theoretical or a practical point
of view； judges according to a priori principles； and then it is clear
that although it is in the first point of view inpetent to
establish certain propositions positively； which； however； do not
contradict it； then； as soon as these propositions are inseparably
attached to the practical interest of pure reason； it must accept
them； though it be as something offered to it from a foreign source；
something that has not grown on its own ground； but yet is
sufficiently authenticated； and it must try to pare and connect
them with everything that it has in its power as speculative reason。
It must remember； however； that these are not additions to its
insight； but yet are extensions of its employment in another；
namely； a practical aspect； and this is not in the least opposed to
its interest； which consists in the restriction of wild speculation。
Thus； when pure speculative and pure practical reason are bined
in one cognition； the latter has the primacy； provided； namely； that
this bination is not contingent and arbitrary； but founded a priori
on reason itself and therefore necessary。 For without this
subordination there would arise a conflict of reason with itself；
since； if they were merely co…ordinate； the former would close its
boundaries strictly and admit nothing from the latter into its domain；
while the latter would extend its bounds over everything and when
its needs required would seek to embrace the former within them。 Nor
could we reverse the order and require pure practical reason to be
subordinate to the speculative； since all interest is ultimately
practical； and even that of speculative reason is conditional； and
it is only in the practical employment of reason that it is plete。
IV。 The Immortality of the Soul as a Postulate of
Pure Practical Reason。
The realization of the summum bonum in the world is the necessary
object of a will determinable by the moral law。 But in this will the
perfect accordance of the mind with the moral law is the supreme
condition of the summum bonum。 This then must be possible； as well
as its object； since it is contained in the mand to promote the
latter。 Now； the perfect accordance of the will with the moral law
is holiness； a perfection of which no rational being of the sensible
world is capable at any moment of his existence。 Since；
nevertheless； it is required as practically necessary； it can only
be found in a progress in infinitum towards that perfect accordance；
and on the principles of pure practical reason it is necessary to
assume such a practical progress as the real object of our will。
Now； this endless progress is only possible on the supposition of an
endless duration of the existence and personality of the same rational
being （which is called the immortality of the soul）。 The summum bonum；
then； practically is only possible on the supposition of the
immortality of the soul； consequently this immortality； being
inseparably connected with the moral law； is a postulate of pure
practical reason （by which I mean a theoretical proposition； not
demonstrable as such； but which is an inseparable result of an
unconditional a priori practical law。
This principle of the moral destination of our nature； namely；
that it is only in an endless progress that we can attain perfect
accordance with the moral law； is of the greatest use； not merely
for the present purpose of supplementing the impotence of
speculative reason； but also with respect to religion。 In default of
it； either the moral law is quite degraded from its holiness； being
made out to be indulgent and conformable to our convenience； or else
men strain their notions of their vocation and their expectation to an
unattainable goal； hoping to acquire plete holiness of will； and so
they lose themselves in fanatical theosophic dreams； which wholly
contradict self…knowledge。 In both cases the unceasing effort to
obey punctually and thoroughly a strict and inflexible mand of
reason； which yet is not ideal but real； is only hindered。 For a
rational but finite being； the only thing possible is an endless
progress from the lower to higher d