In treating the subjects about which I shall write to you in these letters or essays, it will be therefore necessary to distinguish genuine and pure theism from the unnatural and profane mixtures of human imagination—what we can know of God from what we cannot know. This is the more necessary, too, because, whilst true and false notions about God and religion are blended together in our minds under one specious name of science, the false are more likely to make men doubt of the true, as it often happens, than to persuade men that they are true themselves. Now, in order to this purpose, nothing can be more effectual than to go to the root of error, of that primitive error which encourages our curiosity, sustains our pride, fortifies our prejudices, and gives pretence to delusion. This primitive error consists in the high opinion we are apt to entertain of the human mind, though it holds, in truth, a very low rank in the intellectual system. To cure this error we need only turn our eyes inward, and contemplate impartially what passes there from the infancy to the maturity of the mind. Thus it will not be difficult, and thus alone it is possible, to discover the true nature of human knowledge—how far it extends, how far it is real, and where and how it begins to be fantastical. Such an inquiry, if it cannot check the presumption nor humble the pride of metaphysicians, may serve to undeceive others. Locke pursued it; he grounded all he taught on the phenomena of Nature; he appealed to the experience and conscious knowledge of every one, and rendered all he advanced intelligible. Leibnitz, one of the vainest and most chimerical men that ever got a name in philosophy, and who is often so unintelligible that no man ought to believe he understood himself, censured Locke as a superficial philosopher. What has happened? The philosophy of one has forced its way into general approbation, that of the other has carried no conviction and scarce any information to those who have misspent their time about it. To speak the truth, though it may seem a paradox, our knowledge on many subjects, and particularly on those which we intend here, must be superficial to be real. This is the condition of humanity. We are placed, as it were, in an intellectual twilight, where we discover but few things clearly, and none entirely, and yet see just enough to tempt us with the hope of making better and more discoveries. Thus flattered, men push their inquiries on, and may be properly enough compared to Ixion, who “imagined he had Juno in his arms whilst he embraced a cloud.”