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have not even used the Connecticut caution of declaring； as is done
in their blue laws； that the laws of God shall be the laws of their
land； except where their own contradict them； but they swallow the
yea and nay together。 Finally； in answer to Fortescue Aland's
question why the ten commandments should not now be a part of the
common law of England？ we may say they are not because they never
were made so by legislative authority； the document which has imposed
that doubt on him being a manifest forgery。
CLASSIFICATION IN NATURAL HISTORY
_To Dr。 John Manners_
_Monticello； February 22； 1814_
SIR； The opinion which； in your letter of January 24； you
are pleased to ask of me； on the comparative merits of the different
methods of classification adopted by different writers on Natural
History； is one which I could not have given satisfactorily； even at
the earlier period at which the subject was more familiar； still
less； after a life of continued occupation in civil concerns has so
much withdrawn me from studies of that kind。 I can； therefore；
answer but in a very general way。 And the text of this answer will
be found in an observation in your letter； where； speaking of
nosological systems； you say that disease has been found to be an
unit。 Nature has； in truth； produced units only through all her
works。 Classes； orders； genera； species； are not of her work。 Her
creation is of individuals。 No two animals are exactly alike； no two
plants； nor even two leaves or blades of grass； no two
crystallizations。 And if we may venture from what is within the
cognizance of such organs as ours； to conclude on that beyond their
powers； we must believe that no two particles of matter are of exact
resemblance。 This infinitude of units or individuals being far
beyond the capacity of our memory； we are obliged； in aid of that； to
distribute them into masses； throwing into each of these all the
individuals which have a certain degree of resemblance； to subdivide
these again into smaller groups； according to certain points of
dissimilitude observable in them； and so on until we have formed what
we call a system of classes； orders； genera and species。 In doing
this； we fix arbitrarily on such characteristic resemblances and
differences as seem to us most prominent and invariable in the
several subjects； and most likely to take a strong hold in our
memories。 Thus Ray formed one classification on such lines of
division as struck him most favorably； Klein adopted another； Brisson
a third； and other naturalists other designations； till Linnaeus
appeared。 Fortunately for science； he conceived in the three
kingdoms of nature； modes of classification which obtained the
approbation of the learned of all nations。 His system was
accordingly adopted by all； and united all in a general language。 It
offered the three great desiderata： First； of aiding the memory to
retain a knowledge of the productions of nature。 Secondly； of
rallying all to the same names for the same objects； so that they
could communicate understandingly on them。 And Thirdly； of enabling
them； when a subject was first presented； to trace it by its
character up to the conventional name by which it was agreed to be
called。 This classification was indeed liable to the imperfection of
bringing into the same group individuals which； though resembling in
the characteristics adopted by the author for his classification； yet
have strong marks of dissimilitude in other respects。 But to this
objection every mode of classification must be liable； because the
plan of creation is inscrutable to our limited faculties。 Nature has
not arranged her productions on a single and direct line。 They
branch at every step； and in every direction； and he who attempts to
reduce them into departments； is left to do it by the lines of his
own fancy。 The objection of bringing together what are disparata in
nature； lies against the classifications of Blumenbach and of Cuvier；
as well as that of Linnaeus； and must forever lie against all。
Perhaps not in equal degree； on this I do not pronounce。 But neither
is this so important a consideration as that of uniting all nations
under one language in Natural History。 This had been happily
effected by Linnaeus； and can scarcely be hoped for a second time。
Nothing indeed is so desperate as to make all mankind agree in giving
up a language they possess； for one which they have to learn。 The
attempt leads directly to the confusion of the tongues of Babel。
Disciples of Linnaeus； of Blumenbach； and of Cuvier； exclusively
possessing their own nomenclatures； can no longer communicate
intelligibly with one another。 However much； therefore； we are
indebted to both these naturalists； and to Cuvier especially； for the
valuable additions they have made to the sciences of nature； I cannot
say they have rendered her a service in this attempt to innovate in
the settled nomenclature of her productions； on the contrary； I think
it will be a check on the progress of science； greater or less； in
proportion as their schemes shall more or less prevail。 They would
have rendered greater service by holding fast to the system on which
we had once all agreed； and by inserting into that such new genera；
orders； or even classes； as new discoveries should call for。 Their
systems； too； and especially that of Blumenbach； are liable to the
objection of giving too much into the province of anatomy。 It may be
said； indeed； that anatomy is a part of natural history。 In the
broad sense of the word； it certainly is。 In that sense； however； it
would comprehend all the natural sciences； every created thing being
a subject of natural history in extenso。 But in the subdivisions of
general science； as has been observed in the particular one of
natural history； it has been necessary to draw arbitrary lines； in
order to accommodate our limited views。 According to these； as soon
as the structure of any natural production is destroyed by art； it
ceases to be a subject of natural history； and enters into the domain
ascribed to chemistry； to pharmacy； to anatomy； &c。 Linnaeus' method
was liable to this objection so far as it required the aid of
anatomical dissection； as of the heart； for instance； to ascertain
the place of any animal； or of a chemical process for that of a
mineral substance。 It would certainly be better to adopt as much as
possible such exterior and visible characteristics as every traveller
is competent to observe； to ascertain and to relate。 But with this
objection； lying but in a small degree； Linnaeus' method was
received； understood； and conventionally settled among the learned；
and was even getting into common use。 To disturb it then was
unfortunate。 The new system attempted in botany； by Jussieu； in
mineralogy； by Hauiy； are subjects of the same regret； and so also
the no…system of Buffon； the great advocate of individualism in
opposition to classification。 He would carry us back to the days and
to the confusion of Aristotle and Pliny； give up the improvements of
twenty centuries； and co…operate with the neologists in rendering the
science of one generation useless to the next by perpetual changes of
its language。 In botany； Wildenow and Persoon have incorporated into
Linnaeus the new discovered plants。 I do not know whether any one
has rendered us the same service as to his natural history。 It would
be a very acceptable one。 The materials furnished by Humboldt； and
those from New Holland particularly； require to be digested into the
Catholic system。 Among these； the Ornithorhyncus mentioned by you；
is an amusing example of the anomalies by which nature sports with
our schemes of classification。 Although with out mammae； naturalists
are obliged to place it in the class of mammiferae； and Blumenbach；
particularly； arranges it in his order of Palmipeds and toothless
genus； with the walrus and manatie。 In Linnaeus' system it might be
inserted as a new genus between the anteater and manis； in the order
of Bruta。 It seems； in truth； to have stronger relations with that
class than any other in the construction of the heart； its red and
warm blood； hairy integuments； in being quadruped and viviparous； and
may we not say； in its _tout ensemble_； which Buffon makes his sole
principle of arrangement？ The mandible； as you observe； would draw
it towards the birds； were not this characteristic overbalanced by
the weightier ones before mentioned。 That of the Cloaca is
equivocal； because although a character of birds； yet some mammalia；
as the beaver and sloth； have the rectum and urinary passage
terminating at a common opening。 Its ribs also； by their number and
structure； are nearer those of the bird than of the mammalia。 It is
possible that further opportunities of examination may discover the
mammae。 Those of the Opossum are a