All writers on the movement of illumination in France in the eighteenth century, call our attention to the quick transformation, which took place after the middle of the century, of a speculative or philosophical agitation into a political or social one.  Readers often find some difficulty in understanding plainly how or why this metamorphosis was brought about.  The metaphysical question which men were then so fond of discussing, whether matter can think, appears very far removed indeed from the sphere of political conceptions.  The psychological question whether our ideas are innate, or are solely given to us by experience through the sensations, may strike the publicist as having the least possible to do with the type of a government or the aims of a community.  Yet it is really the conclusions to which men come in this region, that determine the quality of the civil sentiment and the significance of political organisation.  The theological doctors who persecuted De Prades for suggestions of Locke’s psychology, and for high treason against Cartesianism, were guided by a right instinct of self-preservation.  De Maistre, by far the most acute and penetrating of the Catholic school, was never more clear-sighted than when he made a vigorous and deliberate onslaught upon Bacon, the centre of his movement against revolutionary principles.[158]

As we have said before, the immediate force of speculative literature hangs on practical opportuneness.  It was not merely because Bacon and Hobbes and Locke had written certain books, that the Encyclopaedists, who took up their philosophic succession, inevitably became a powerful political party, and multiplied their adherents in an increasing proportion as the years went on.  From various circumstances the attack acquired a significance and a weight in France which it had never possessed in England.  For one thing, physical science had in the interval taken immense strides.  This both dwarfed the sovereignty of theology and theological metaphysics, and indirectly disposed men’s minds for non-theological theories of moral as well as of physical phenomena.  In France, again, the objects of the attack were inelastic and unyielding.  Political speculation in England followed, and did not precede, political innovation and reform.  In France its light played round institutions which were too deeply rooted in absolutism and privilege to be capable of substantial modification.  Deism was comparatively impotent against the Church of England, first, because it was an intellectual movement, and not a social one; second, because the constitutional doctrines of the church were flexible.  Deism in the hands of its French propagators became connected with social liberalism, because the Catholic church in those days was identified with all the ideas of repression.  And the tendencies of deism in France grew more violently destructive, not only because religious superstition was grosser, but because that superstition was incorporated in a strong and inexpansible social structure.