Abstract of Logic, Book 2 · Chapter 24 – Chapter 25
CHAP. XXIV. Of Demonſtration foreign, or That and Regreſs.
Ax. 1. NOW of Demonſtration, That the one is from the Effect, and the other from the remote Cauſe.
Ax. 2. Of which that collects the Cauſe from the Effect Senſible; and this the Effect from the remote Cauſe.
1. §. For Example; If any one riſing ſomething later than uſual, ſhould ſee the Walls of his Chamber colluſtrated with the Sun-Beams, and collect from thence that the Sun had been ſometime riſen; This would be from the ſenſible Effect. From the remote Cauſe, this, viz. Plants have not a Senſitive Soul; and therefore they don't breath, &c.
Ax. 3. Now that from the Effect may be as well Affirmed as Denyed. The remote Cauſe always Deny'd and Concluded in the Second Figure in Cameſtres.
And, therefore, as we collect Plants live, becauſe they grow, and are nouriſhed; ſo alſo may we that Stones do not; becauſe they neither grow, nor are nouriſhed, &c. And as from an unequal Concitated Pulſe of the Arteries we collect that there is a Fever. So alſo from an equal and ſedate, that there is none; or that there is an Immunity from a Fever, &c. But it does not follow that all Animals breathe, becauſe they have a Senſitive Soul, altho' it does, that no Plant does, becauſe it has not; becauſe having a Senſitive Soul is not the next Cauſe of Breathing, &c.
3. §. Now of theſe two Species's of Demonſtration, the firſt is much nobler than the laſt; Firſt, becauſe it has more neceſſary Propoſitions, conſiſting of the ſame Terms of which does the Demonſtration foreign. Secondly, begets Knowledge tho' not ſimply; yet ſuch as is in its Genus perfect. For a Cauſe can no other ways be known but by its Effect. Thirdly, it is framed in the firſt Figure, and may alſo be affirmed. Whereas Demonſtration from the Cauſe remote conſiſts of leſs neceſſary Propoſitions, and not immediate; Neither does it beget Knowledge in its own kind perfect, neither can it be fram'd in the firſt Figure, &c. Both yet beget ſuch a Knowledge as that we may know whether the thing is or is not, &c.
Ax. 4. As ſoon then as the Cauſe is deprehended from the ſenſible Effect, a Compariſon is inſtituted between that Cauſe and the Effect. And when the Mind, by its Sagacity, diſcovers that that Cauſe is the Cauſe of that Effect; then a Regreſs is made from the Cauſe to the Effect, by a Demonſtration foreign, &c.
1. §. Sometimes the Effect is unknown, and the Cauſe known; and then, immediately is made uſe of the Demonſtration foreign. Sometimes the Effect's perceiv'd, and Cauſe unknown; and then firſt, the Cauſe from the Effect, and then the Effect from the Cauſe is to be demonſtrated. And this ſort of Demonſtration is uſually call'd by the Latins, a Regreſs, in which the Cauſes are firſt to be inveſtigated by the Effects; And then from the true Knowledge of thoſe Cauſes is to be deriv'd a true and perfect Knowledge of thoſe Effects; whereby we not only know that the Effects be (of which our Senſes are Judges) but alſo why and what they be; further than which our Minds cannot reach. And thus much may ſuffice for an Account of true Syllogiſm.
Notes and Obſervations from the Learned Heereboord in Relation to this 24th Chapter.
WHEN the Demonſtration from the remote Cauſe is ſaid to be always Negative, by the Ingenious Author it is to be underſtood with this Reſtriction, viz. when it is larger than the Effect; and not reciprocated with it; as in the Inſtance which he has given; which is very true. But ſometimes it may happen that the remote Cauſe may be equal to, and not larger than the Effect, and then it is reciprocated with it; and may be affirmed; as in this Inſtance. Thoſe things which are Animals Vegetative are nouriſhed: Plants are Animals Vegetative; and therefore they are nouriſhed: Wherein the middle Term is the Remote Cauſe: For the next is the Nutritive Faculty; and yet the Syllogiſm proceeds in the firſt Figure, and is affirmed; becauſe the remote Cauſe is adequate to the Effect; and reciprocate with it: For whatſoever is nouriſhed, has a Vegetative Soul; and whatſover is not, has not, &c.
CHAP. XXV. Of Sophiſm.
Ax. 1. NEXT follows Syllogiſm foreign, or Fallacious, which counterfeiting a Shew of the True, produces Error, or an Ignorance of Depraved Diſpoſition.
COMMENTARY.
1. §. Now Precepts concerning this are very neceſſary in Logick, for Fear, leſt others ſhould impoſe upon us. For he that is liable to be deceiv'd by another, and is not aware of it, may alſo be deceiv'd by himſelf.
2. §. But (ſay they who wo'n't admit of the Doctrin of Fallacious Syllogiſm in Logick) the Right is the Rule both of it ſelf and the Wrong; and one Oppoſite is ſufficient to diſcern the other by. Book 1. An. Cap. 1. Whence they conclude, that the Precepts of true Syllogiſm are enough to detect the Fallacies of the other by; And ſo that this Part of Logick is nothing worth. But it is not ſo: For the Right is then the Rule of the Wrong, when the wrong, as wrong, is oppos'd to it. And the Knowledge of one Oppoſite is then ſufficient for the Diſcernment of the other; when the oppoſed, as oppoſed, is compoſed with it. But now when the Oblique puts on the Form of the Right, or one Oppoſite that of the other, 'tis not every ſort of Knowledge of the Right, that does ſerve to diſtinguiſh the Wrong from it; nor the one Oppoſite to underſtand the Difference of the other by. Now a Fallacious Sophiſm is not only Vicious, but alſo puts on the Shew of Good: And therefore thoſe Precepts of Syllogiſm, which we have already laid down, are not ſufficient fully to underſtand the Tricks of Sophiſters by. Why? Becauſe it is not enough to know the Fault of the Fallacious Syllogiſm; but over-and-above, we muſt take off the Appearance of the true, and plainly demonſtrate from which Box of Fallacies that Varniſh was taken, whereby the Sophiſter has ſet off his Vicious Syllogiſm. And firſt of thoſe Fallacies which are committed in Word.