The principle that separates the two is not to be found in the symptoms, nor in fact in the causes, but in the spatial solidity of the body alone, in what might be termed the density of the interior landscape: For as the outward man is fram'd with parts obvious to sense, so, without doubt, the inward man consists of a due series, and, as it were, a Fabrick of the Spirits, to be viewed only by the Eye of Reason; and as this is nearly join'd, and, as it were, united with the Constitution of the Body, so much the more easily or more difficultly the Frame of it is disorder'd, by how much the Constitutive Principles that are allotted us by nature, are more or less firm.