In the natural sciences...

In the natural sciences, we commonly employ analogical models in an effort to comprehend the real essences of which we are constitutionally ignorant. [Essay IV xvi 10-12] In addition to all of these legitimate grounds for guidance, the faculty of judgment commonly falls victim to unworthy and unsupported claims to its assent.

Someone may demand that I assent to the truth of a proposition only because it is defended by some putative authority, in the absence of any proof of its falsity, or solely because it agrees with other opinions I already hold. But since all of these matters are formally irrelevant to the truth of the proposition in question, Locke supposed, they should have no bearing on my assent.

The only legitimate grounds for agreeing with someone are demonstrative knowledge and probable judgment, both of which ultimately rest only upon "the nature of Things themselves." [Essay IV xvii 19-22] ©1999-2002 Garth Kemerling.Last modified 27 October 2001.Questions, comments, and suggestions may be sent to: God Like many of his English contemporaries, Locke was deeply interested in matters of faith and religion.

Keenly aware of the theological controversies of the day, he developed and defended views of his own that proved influential on the Deists of the next generation. Although knowledge of God is vital for human life and practical conduct, on Locke's view, it cannot be grounded legitimately on the supposedly universal possession of an innate idea.

[Essay I iv 8-9] Although he claimed to demonstrate the existence of God as the only reasonable explanation for the emergence of thought in an otherwise material world, Locke warned against an excessive reliance upon non-rational considerations in the defense of particular religious doctrines.

Thinking Substances We form our complex ideas of spirits, Locke held, by adding the notions of a variety of cognitive powers (themselves acquired, as ideas of reflection, from careful observation of our own mental operations) to the abstract idea of substance in general.

Since this is perfectly analogous to the way we form complex ideas of bodies from our ideas of sensation, the results are perfectly comparable: although we are familiar with both bodies and spirits in our ordinary experience, the real essences of thinking and moving substances alike remain forever unknowable.