ctive speculation," as Duehring terms it, which
derives laws of far-reaching importance from inconspicuous facts; this,
as Galileo himself recognizes, the distinctive gift of the investigator.
Galileo anticipates Descartes in regard to the subjective character of
sense qualities and their reduction to quantitative distinctions,[2] while
he shares with him the belief in the typical character of mathematics and
the mechanical theory of the world. The truth of geometrical propositions
and demonstrations is as unconditionally certain for man as for God, only
that man learns them by a discursive process, whereas God's intuitive
understanding comprehends them with a glance and knows more of them than
man. The book of the universe is written in mathematical characters; motion
is the fundamental phenomenon in the world of matter; our knowledge reaches
as far as phenomena are measurable; the qualitative nature of force, back
of its quantitative determinations, remains unknown to us. When Galileo
maintains that the Copernican theory is philosophically true and not merely
astronomically useful, thus interpreting it as more than a hypothesis,
he is guided by the conviction that the simplest explanation is the most
probable one, that truth and beauty are one, as in general he concedes
a guiding though not a controlling influence in scientific work to the
aesthetic demand of the mind for order, harmony, and unity in nature, to
correspond to the wisdom of the Creator.

[Footnote 1: Cf. Natorp's essay on Galileo, in vol. xviii. of the
_Philosophische Monatshefte_, 1882.]

[Footnote 1: This doctrine is developed by Galileo in the controversial
treatise against Padre Grassi, _The Scales (Il Saggiatore_, 1623, in the
Florence edition of his collected works, 1842 _seq_., vol. iv. pp.
149-369; cf. Natorp, _Descartes' Erkenntnisstheorie_, 1882, chap. vi.). In
substance, moreover, this doctrine is found, as Heussler remarks, _Baco_,
p. 94, in Bacon himself, in _Valerius Terminus (Works_, Spedding, vol. iii.
pp. 217-252.)]

One of the most noted and influential among the contemporaries, countrymen,
and opponents of Descartes, was the priest and natural scientist, Petrus
Gassendi,[1] from 1633 Provost of Digne, later for a short period professor
of mathematics at Paris. His renewal of Epicureanism, to which he was
impelled by temperament, by his reverence for Lucretius, and by the
anti-Aristotelian tendency of his thinking, was of far more imp