or what is thought of? Psychology usually goes to work in this
abstract fashion; but such a mode of procedure is hopeless,--as
hopeless as the analogous instance by which the wits of old were
wont to typify any particularly fruitless undertaking,--namely, the
operation of milking a he-goat into a sieve. No milk comes, in the
first place, and even that the sieve will not retain! There is a loss
of nothing twice over. Like the man milking, the inquirer obtains no
milk in the first place; and, in the second place, he loses it,
like the man holding the sieve.... Our Scottish philosophy, in
particular, has presented a spectacle of this description. Reid
obtained no result, owing to the abstract nature of his inquiry, and
the nothingness of his system has escaped through all the sieves of
his successors." [16]

[Footnote 15: _Essay_, Book I. Chap. 1, Sect. 7.]

[Footnote 16: _Institutes of Metaphysic_, p. 301.]

Leibnitz's metaphysical speculations are scattered through a wide
variety of writings, many of which are letters to his contemporaries.
These Professor Erdmann has incorporated in his edition of the
Philosophical Works. Beside these we may mention, as particularly
deserving of notice, the "Meditationes de Cognitione, Veritate et
Ideis", the "Systeme Nouveau de la Nature", "De Primae Philosophiae
Emendatione et de Notione Substantiae", "Reflexions sur l'Essai de
l'Entendement humain", "De Rerum Originatione Radicali", "De ipsa
Natura", "Considerations sur la Doctrine d'un Esprit universel",
"Nouveaux Essais sur l'Entendement humain", "Considerations sur le
Principe de Vie". To these we must add the "Theodicee" (though more
theological than metaphysical) and the "Monadologie", the most