I Expect you should here urge on your Friends behalf, That the study of Physicks has one Prerogative, (above that of Divinity,) which, as it is otherwise a great Excellency, so does much add to the Delightfulness of it. I mean, the Certainty, and Clearness, and the thence resulting Satisfactoriness of our Knowledge of Physical, in comparison of any we can have of Theological matters, whose being Dark and Uncertain, the Nature of the things themselves, and the numerous Controversies of differing Sects about them, sufficiently manifest.
But upon this Subject, divers things are to be consider’d.
For first, as to the Fundamental and Necessary Articles of Religion, I do not admit the Allegation, but take those Articles to be both Evident, and capable of a Moral Demonstration. And if there be any Articles of Religion, for which a Rational and Cogent Proof cannot be brought, I shall for that very reason conclude, that such Articles are not absolutely Necessary to be believ’d; since it seems no way reasonable to imagine, that God having been pleased to send not onely his Prophets and his Apostles, but his onely Son into the World, to promulgate to Mankind the Christian Religion, and both to cause it to be consign’d to writing, that it may be known, and to alter the course of Nature by numerous Miracles, that it might be believ’d; it seems not reasonable, I say, to imagine, that he should not propose those Truths, which he in so wonderful and so solemn a manner recommended, with at least so much Clearness, as that studious and well-dispos’d Readers may certainly understand such as are necessary for them to believe.
- Though I will not here engage my self in a Disquisition of the several kinds, or, if you please, Degrees, of Demonstration, (which yet is a Subject that I judge far more considerable than cultivated,) yet I must tell you, that as a Moral certainty (such as we may attain about the Fundamentals of Religion) is enough in many cases for a wise man, and even a Philopher to acquiesce in; so that Physical Certainty, which is pretended for the Truths demonstrated by Naturalists, is, even where ‘tis rightfully claim’d, but an inferiour kind or degree of certainty, as Moral certainty also is. For even Physical Demonstrations can beget but a Physical Certainty, (that is, a Certainty upon supposition that the Principles of Physick be true,) not a Metaphysical Certainty, (wherein ‘tis absolutely impossible, that the thing believ’d should be other than true.) For instance, All the Physical Demonstrations of the Antients about the causes of particular Phaenomena of Bodies, suppose, that ex nihilo nihil fit; and this may readily be admitted in a Physical sense, because according to the course of Nature, no Body can be produc’d out of Nothing, but speaking universally it may be false, as Christians generally, and even the Cartesian Naturalists, asserting the Creation of the World, must believe, that, de facto, it is. And so whereas Epicurus does, I remember, prove, that a Body once dead cannot be made alive again, by reason of the dissipation and dispersion of the Atoms, ‘twas, when alive, compos’d of; though all men will allow this assertion to be Physically demonstrable, yet the contrary may be true, if God’s Omnipotence intervenes, as all the Philosophers that acknowledge the Authority of the New Testament, where Lazarus and others are recorded to have been raised from the dead, must believe, that it actually did appear, and even all unprejudic’d Reasoners must allow it to be Possible, there being no Contradiction impli’d in the Nature of the thing. But now to affirm, that such things as are indeed Contradictories cannot be both true, or, that factum infectum reddi non potest, are Metaphysical Truths, which cannot possibly be other than true, and consequently beget a Metaphysical and absolute Certainty. And your Master Cartesius was so sensible of a dependance of Physical Demonstrations upon Metaphysical Truths, that he would not allow any certainty not onely to them, but even to Geometrical Demonstrations, till he had evinc’d, that there is a God, and that he cannot deceive men that make use of their Faculties aright.
To which I may add, that even in many things that are look’d upon as Physical Demonstrations, there is really but a Moral Certainty. For when, for instance, Des-Cartes and other Modern Philosophers, take upon them to demonstrate, That there are divers Comets that are not Meteors, because they have a Parallax lesser than that of the Moon, and are of such a bigness, and some of them move in such a Line, &c. ‘tis plain, that divers of these Learned men had never the opportunity to observe a Comet in their Lives, but take these Circumstances upon the credit of those Astronomers that had such Opportunities. And though the Inferences, as such, may have a Demonstrable Certainty; yet the Premisses they are drawn from having but an Historical one, the presumed Physico-Mathematical Demonstration can produce in a wary mind but a Moral Certainty, and not the greatest neither of that kind that is possible to be attain’d; as he will not scruple to acknowledge, that knows by experience, how much more difficult it is, than most men imagine, to make Observations about such nice Subjects, with the exactness that is requisite for the building of an undoubted Theory upon them. And there are I know not how many things in Physicks, that men presume they believe upon Physical and Cogent Arguments, wherein they really have but a Moral assurance; which is a Truth heeded by so few, that I have been invited to take the more particular notice of them in other Papers, written purposely to show the doubtfulness and incompleatness of Natural Philosophy; of which Discourse, since you may command a sight, I shall not scruple to refer you thither for the Reasons of my affirming here, that the most even of the modern Virtuosi are wont to fancy more of Clearness and Certainty in their Physical Theories, than a Critical Examiner will find. Onely that you may not look upon this as a put off, rather than a reference, I will here touch upon a couple of Subjects, which men are wont to believe to be, and which indeed ought to be, the most throughly understood; I mean the Nature of Body in general, and the Nature of Sensation.