Horst Steinke
218
the imagination with the help of the senses, or [3
rd
kind:] as Sub-
stance
505
, apprehended by means of the intellect.
This contrast is woven through the entire letter, or, to mix
metaphors, executed as multiple variations on a theme. Between
these two epistemic poles that carry the main argumentative bur-
den, however, the remaining component of his epistemic struc-
ture, that is, the second kind of knowledge, is not absent either in
the letter. He refers to it by the term of «mental constructs», as
applicable to the notions of «Time», «Measure», and «Number».
These notions have their origin, not in the sense(d) data, but in
the «Modes» of «Duration» and «Quantity» understood as «the
affections of Substance», thus implicitly accessible only
via
the
third kind of knowledge. They serve as «aids to the imagination»,
and function, in effect, as «modes of thinking, […] modes of im-
agining». Spinoza’s example ostensibly is meant to provide phys-
ical proof of his infinity thesis, but, conversely, the physics, and
mathematics, of “fluid dynamics” is at the same time framed di-
rectly in terms of metaphysics
506
: «[…] if anyone were to attempt
to determine all the motions of matter that have ever been, re-
ducing them and their duration to a definite number and time, he
would be attempting to deprive corporeal Substance […] of its
affections, and to bring it about that Substance should not pos-
sess the nature which it does possess». The correct inference or
deduction of the «infinite» variation of the velocity of the fluid
(i.e. acceleration/deceleration), thus, for Spinoza, primarily fol-
lows from the third kind of knowledge; once this is estab-
lished
507
, it can be verified from the “experimental” data. We
have before us an epistemic compartmentalization, and stratifica-
tion, that is isomorphic to that underlying Spinoza’s biblical-
criticism in
TTP;
in the pursuit of science, physicists
508
, lacking
the benefit of «intuitive knowledge»
–
who, in Spinoza’s words,
«because of their ignorance of the true nature of reality, have de-
nied the actual existence of the infinite»
–
epistemologically, find