3. D^r _Moore_ maketh substance to be the genus, and spirit and body to be the two species, so that body and spirit are of one generical Identity, and so there must of necessity some certain specific difference betwixt them be assigned and proved, or else the division is vitious, and the property of spirit not proved, and so their opinion of spirit falls totally to the ground. For we affirm (and shall prove) that though a difference be imagined and supposed, yet it was never yet sufficiently proved, for _omnia supposita, non sunt vera_, otherwise all the impossible figments and vain _Chimæras_ of melancholy and doting persons might pass for true Oracles: but it is one thing truly to understand, and another thing to imagine and fancy what indeed is not, nor ever was. And though the supposition seem never so probable and like, yet it will but at the best infer the possibility of such an imagined difference, but not prove it really to be so, and therefore here we shall retort the Doctors Axiom against him, which is this: “Whatsoever is unknown to us, or is known but as meerly possible, is not to move us or determine us any way, or make us undetermined; but we are to rest in the present light and plain determination of our own faculties.” Now that a spirit is penetrable and indiscerpible, may be imagined as possible to the fancies of some, but cannot be clearly intelligible to any sober mind; for to imagine, and to understand, are faculties that are very different, and however if such a difference be conceived as possible (which cannot enter the narrow gate of my Intellect) yet the difference of being penetrable and indiscerpible, is not to move us to determine that a spirit hath those distinct properties from bodies, because they are but known to us as meerly possible. And therefore that these two differences of penetrability and indiscerpibility assigned by D^r _Moore_, are not sufficiently proved to be so, we shall give these reasons. 1. If bodies in the ultimate act of nature can penetrate themselves and one another, as Helmont and D^r _Glisson_ do strongly labour to prove, then penetrability is not the proper difference of spirit from body, because then common to them both. 2. But if it be taken for a truth (and the one of necessity must be true) that bodies do not, or can possibly penetrate themselves or one another, as the common tenent holdeth, and seemeth most agreeable to verity, for it is simply unintelligible and impossible to conceive, that two Cubes (suppose of Marble or Metal) should penetrate one another, and yet but to have the dimensions of one, and to possess no greater space than the one did formerly fill: And if this be impossible and unintelligible in respect of bodies, whose properties, aptitudes, affections and modifications are apparent to our senses, then must it be more impossible and unintelligible in substances supposed to be meerly incorporeal, because they must needs be more pure and perfect, and