The operations and maladies of the intellect.
Though no actual knowledge be so immediate as to be without the mediation of the sense and fantasy, yet supposing these, knowledge is distinguished into immediate and mediate. The immediate is when the being, quality, &c. of a thing, or the truth of a proposition, is known immediately in itself by its proper evidence. Mediate knowledge is when the being of a thing, or the truth of a proposition, is known by the means of some other intervenient thing or proposition, whose evidence affordeth us a light to discern it.
The understanding is much more satisfied when it can see things and truths immediately in their proper evidence. But when it cannot, it is glad of any means to help it.
The further we go in the series of means, (knowing one thing by another, and that by another, and so on,) the more unsatisfied the understanding is, as apprehending a possibility of mistake, and a difficulty in escaping mistake in the use of so many media.
When the evidence of one thing in its proper nature showeth us another, this is to know by mere discourse or argument.
When the medium of our knowing one thing is the credibility of another man's report that knoweth it, this is (though a discourse or argument too, yet) in special, called, belief; which is strong or weak, certain or uncertain, as the evidence of the reporter's credibility is certain or uncertain, and our apprehension of it strong or weak.
In both cases, the understanding's fault is either an utter privation of the act, or disposition to it; or else a privation of the rectitude of the act. When it should know by the proper evidence of the thing, the privation of its act is called ignorance or nescience, and the privation of its rectitude is called error (which differ as not seeing, and seeing falsely.) When it should know by testimony, the privation of its act is simple unbelief, or not believing, and the privation of its rectitude is either disbelief, when they think the reporter erreth, or misbelief, when it believeth a testimony that is not to be believed.
So that you see by what is said, that the diseases of the mind to be cured, are, 1. Mere ignorance. 2. Error; thinking truth to be falsehood, and falsehood truth. 3. Unbelief. 4. Disbelief. And 5. Misbelief.
Rom. viii. 5-7.
But as the goodness is of chief regard in the object, so the discerning of the truth about good and evil, is the chiefest office of the understanding. And therefore its disesteem of God, and glory, and grace, and its misesteem of the fleshly pleasure, and worldly prosperity, wealth, and honour, is the principal malady of the mind.