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114 treated of the association of ideas; yet having done it there historically, as giving a view of the understanding in this as well as its several other ways of operating, rather than designing there to inquire into the remedies that ought to be applied to it; it will, under this latter consideration, afford other matter of thought to those who have a mind to instruct themselves thoroughly in the right way of conducting their understandings: and that the rather, because this, if I mistake not, is as frequent a cause of mistake and error in us as perhaps anything else that can be named; and is a disease of the mind as hard to be cured as any, it being a very hard thing to convince anyone that things are not so, and naturally so, as they constantly appear to him.

By this one easy and unheeded miscarriage of the understanding, sandy and loose foundations become infallible principles, and will not suffer themselves to be touched or questioned; such unnatural connections become by custom as natural to the mind as sun and light, fire and warmth go together, and so seem to carry with them as natural an evidence as self-evident truths themselves. And where then shall one with hopes of success begin the cure? Many men firmly embrace falsehood for truth; not only because they never thought otherwise, but also because, thus blinded as they have been from the beginning, they never could think otherwise; at least without a vigor of mind able to contest the empire of habit, and look into its own principles; a freedom which few men have the