to be solved； for the systematic representation of the existing
variety of powers。 The logical principle of reason requires us to
produce as great a unity as is possible in the system of our
cognitions； and the more the phenomena of this and the other power are
found to be identical； the more probable does it bee； that they are
nothing but different manifestations of one and the same power；
which may be called； relatively speaking； a fundamental power。 And
so with other cases。
These relatively fundamental powers must again be pared with each
other； to discover； if possible； the one radical and absolutely
fundamental power of which they are but the manifestations。 But this
unity is purely hypothetical。 It is not maintained； that this unity
does really exist； but that we must； in the interest of reason； that
is； for the establishment of principles for the various rules
presented by experience； try to discover and introduce it； so far as
is practicable； into the sphere of our cognitions。
But the transcendental employment of the understanding would lead us
to believe that this idea of a fundamental power is not problematical；
but that it possesses objective reality； and thus the systematic unity
of the various powers or forces in a substance is demanded by the
understanding and erected into an apodeictic or necessary principle。
For； without having attempted to discover the unity of the various
powers existing in nature； nay； even after all our attempts have
failed； we notwithstanding presuppose that it does exist； and may
be； sooner or later； discovered。 And this reason does； not only； as in
the case above adduced； with regard to the unity of substance； but
where many substances； although all to a certain extent homogeneous；
are discoverable； as in the case of matter in general。 Here also
does reason presuppose the existence of the systematic unity of
various powers… inasmuch as particular laws of nature are
subordinate to general laws； and parsimony in principles is not merely
an economical principle of reason； but an essential law of nature。
We cannot understand； in fact； how a logical principle of unity
can of right exist； unless we presuppose a transcendental principle；
by which such a systematic unit… as a property of objects
themselves… is regarded as necessary a priori。 For with what right can
reason； in its logical exercise； require us to regard the variety of
forces which nature displays； as in effect a disguised unity； and to
deduce them from one fundamental force or power； when she is free to
admit that it is just as possible that all forces should be
different in kind； and that a systematic unity is not conformable to
the design of nature？ In this view of the case； reason would be
proceeding in direct opposition to her own destination； by setting
as an aim an idea which entirely conflicts with the procedure and
arrangement of nature。 Neither can we assert that reason has
previously inferred this unity from the contingent nature of
phenomena。 For the law of reason which requires us to seek for this
unity is a necessary law； inasmuch as without it we should not possess
a faculty of reason； nor without reason a consistent and
self…accordant mode of employing the understanding； nor； in the
absence of this； any proper and sufficient criterion of empirical
truth。 In relation to this criterion； therefore； we must suppose the
idea of the systematic unity of nature to possess objective validity
and necessity。
We find this transcendental presupposition lurking in different
forms in the principles of philosophers； although they have neither
recognized it nor confessed to themselves its presence。 That the
diversities of individual things do not exclude identity of species；
that the various species must be considered as merely different
determinations of a few genera； and these again as divisions of
still higher races； and so on… that； accordingly； a certain systematic
unity of all possible empirical conceptions； in so far as they can
be deduced from higher and more general conceptions； must be sought
for； is a scholastic maxim or logical principle； without which
reason could not be employed by us。 For we can infer the particular
from the general； only in so far as general properties of things
constitute the foundation upon which the particular rest。
That the same unity exists in nature is presupposed by
philosophers in the well…known scholastic maxim； which forbids us
unnecessarily to augment the number of entities or principles （entia
praeter necessitatem non esse multiplicanda）。 This maxim asserts
that nature herself assists in the establishment of this unity of
reason； and that the seemingly infinite diversity of phenomena
should not deter us from the expectation of discovering beneath this
diversity a unity of fundamental properties； of which the aforesaid
variety is but a more or less determined form。 This unity； although
a mere idea； thinkers have found it necessary rather to moderate the
desire than to encourage it。 It was considered a great step when
chemists were able to reduce all salts to two main genera… acids and
alkalis； and they regard this difference as itself a mere variety；
or different manifestation of one and the same fundamental material。
The different kinds of earths （stones and even metals） chemists have
endeavoured to reduce to three； and afterwards to two； but still；
not content with this advance； they cannot but think that behind these
diversities there lurks but one genus… nay； that even salts and earths
have a mon principle。 It might be conjectured that this is merely
an economical plan of reason； for the purpose of sparing itself
trouble； and an attempt of a purely hypothetical character； which；
when successful； gives an appearance of probability to the principle
of explanation employed by the reason。 But a selfish purpose of this
kind is easily to be distinguished from the idea； according to which
every one presupposes that this unity is in accordance with the laws
of nature； and that reason does not in this case request； but
requires； although we are quite unable to determine the proper
limits of this unity。
If the diversity existing in phenomena… a diversity not of form （for
in this they may be similar） but of content… were so great that the
subtlest human reason could never by parison discover in them the
least similarity （which is not impossible）； in this case the logical
law of genera would be without foundation； the conception of a
genus； nay； all general conceptions would be impossible； and the
faculty of the understanding； the exercise of which is restricted to
the world of conceptions； could not exist。 The logical principle of
genera； accordingly； if it is to be applied to nature （by which I mean
objects presented to our senses）； presupposes a transcendental
principle。 In accordance with this principle； homogeneity is
necessarily presupposed in the variety of phenomena （although we are
unable to determine a priori the degree of this homogeneity）；
because without it no empirical conceptions； and consequently no
experience； would be possible。
The logical principle of genera； which demands identity in
phenomena； is balanced by another principle… that of species； which
requires variety and diversity in things； notwithstanding their
accordance in the same genus； and directs the understanding to
attend to the one no less than to the other。 This principle （of the
faculty of distinction） acts as a check upon the reason and reason
exhibits in this respect a double and conflicting interest… on the one
hand； the interest in the extent （the interest of generality） in
relation to genera； on the other； that of the content （the interest of
individuality） in relation to the variety of species。 In the former
case； the understanding cogitates more under its conceptions； in the
latter it cogitates more in them。 This distinction manifests itself
likewise in the habits of thought peculiar to natural philosophers；
some of whom… the remarkably speculative heads… may be said to be
hostile to heterogeneity in phenomena； and have their eyes always
fixed on the unity of genera； while others… with a strong empirical
tendency… aim unceasingly at the analysis of phenomena； and almost
destroy in us the hope of ever being able to estimate the character of
these according to general principles。
The latter mode of thought is evidently based upon a logical
principle； the aim of which is the systematic pleteness of all
cognitions。 This principle authorizes me； beginning at the genus； to
descend to the various and diverse contained under it； and in this way
extension； as in the former case unity； is assured to the system。
For if we merely examine the sphere of the conception which
indicates a genus； we cannot discover how far it is possible to
proceed in the division of that sphere； just as it is impossible； from
the consideration of the space occupied by matter； to determine how
far we can proceed in the division of it。 Hence every genus must
contain different species； and these again different subspecies； and
as each of the latter must itself contain a sphere （must be of a
certain ext