102

SKETCH I

Principles and Progrefs of REASON.

SECTION I

PRINCIPLES OF REASON.

Every affirmation, whatever be the subject, is termed a pro

pofition.

Truth and error are qualities of propofitions. A propofition that fays a thing is what it is in reality, is termed a true propofition. A propofition that fays a thing is what it is not in reality, is termed an erroneous propofition.

Our knowledge of what is agreeable and difagreeable in objects is derived from the fenfe of beauty, handled in Elements of Criticifm. Our knowledge of right and wrong in actions, is derived from the moral fenfe, to be handled in the sketch immediately following. Our knowledge of truth and error is derived from various fources.

Our external fenfes are one fource of knowledge: they lay open to us external fubjects, their qualities, their actions, with events produced by thefe actions. The internal fenfes are another fource of knowledge: they lay open to us things paffing in the mind;

thinking,

thinking, for example, deliberating, inclining, refolving, willing, consenting, and other actions; and they alfo lay open to us our emotions and paffions. There is a fenfe by which we perceive the truth of many propofitions; fuch as, That every thing which begins to exift, muft have a caufe; That every effect adapted to fome end or purpose, proceeds from a defigning caufe; and, That every effect adapted to a good end or purpose, proceeds from a defigning and benevolent caufe. A multitude of axioms in every science, particularly in mathematics, are perceived to be equally true. By a peculiar fenfe, of which afterward, we know that there us a Deity. By another fense we know, that the external figns of paffion are the fame in all men; that animals of the fame external appearance, are of the fame fpecies; and that animals of the fame fpecies, have the fame properties (a). By another sense we fee into futurity: we know that the fun will rise to-morrow; that the earth will perform its wonted courfe round the fun; that winter and fummer will follow each other in fucceffion; that a ftone dropt from the hand will fall to the ground; and a thoufand other fuch propofitions.

There are many propofitions, the truth of which is not fo apparent: a process of reafoning is necessary, of which afterward.

Human teftimony is another fource of knowledge. So framed are we by nature, as to rely on human teftimony; by which we are informed of beings, attributes, and events, that never came under any of our fenfes.

The knowledge that is derived from the fources mentioned, is of different kinds. In fome cafes, our knowledge includes abfolute certainty, and produces the higheft degree of conviction: in other cases, probability comes in place of certainty, and the conviction is inferior in degree. Knowledge of the latter kind is diftinguifhed

(e) Book 1. sketch 1

into

into belief, which concerns facts; and opinion, which concerns relations, and other things that fall not under the denomination of facts. In contradiftinction to opinion and belief, that fort of knowledge which includes abfolute certainty, and produces the highest degree of conviction, retains its proper name. To explain what is here faid, I enter into particulars.

The sense of seeing, with very few exceptions, affords knowledge in its proper fenfe. It is not in our power to doubt of the existence of a perfon we fee, touch, and converfe with; and when fuch is cur conftitution, it is a vain attempt to call in question the authority of our sense of seeing, as some writers pretend to do. No one ever called in queftion the existence of internal actions and paffions, laid open to us by internal fenfe; and there is as little ground for doubting of what we fee. The fenfe of feeing, it is true, is not always correct: through different mediums the fame object is feen differently: to a jaundic'd eye every thing appears yellow; and to one intoxicated with liquor, two candles fometimes appear four. But we are never left without remedy in such a case: it is the province of the reafoning faculty, to correct every error of that kind.

its

proper sense; And Nature in for it is evident,

An object of fight, when recalled to mind by the power of memory, is termed an idea or fecondary perception. An original perception, as faid above, affords knowledge in but a fecondary perception affords belief only, this, as in all other inftances, is faithful to truth; that we cannot be fo certain of the existence of an object in its abfence, as when present.

With respect to many abftract propofitions, of which inftances are above given, we have an abfolute certainty and conviction of their truth, derived to us from various fenfes. We can, for example, entertain as little doubt, that every thing which begins to exist, must have a cause, as that the fun is in the firmament; and

as

as little doubt that he will rife to-morrow, as that he is now fet. There are many other propofitions, the truth of which is probable only, not abfolutely certain; as, for example, that things will continue in their ordinary state. That natural operations are performed in the fimplest manner, is an axiom of natural philofophy: it may be probable, but is far from being certain *

In every one of the inftances given, conviction arifes from a fingle act of perception: for which reason, knowledge acquired by means of that perception, not only knowledge in its proper sense, but also opinion and belief, are termed intuitive knowledge. But there are many things, the knowledge of which is not obtained with fo much facility. Propofitions for the most part require a process or operation in the mind, termed reafoning; leading, by certain intermediate fteps, to the propofition that is to be demonstrated or made evident; which, in oppofition to intuitive knowledge, is termed difcurfive knowledge. This procefs or operation must be explained, in order to understand the nature of reasoning. And as reafoning is moftly employ'd in discovering relations, I fhall draw my examples from them. Every propofition concerning relations, is an affirmation of a certain relation between two fubjects. If the relation affirmed appear not intuitively, we must fearch for a third fubject, that appears intuitively to be connected with each of the others, by the relation affirmed: and if fuch a fubject be found, the propofition is demonftrated; for it is

I have given this propofition a place, because it is affumed as an axiom by all writers on natural philofophy. And yet there appears fome room for doubting, whether the conviction we have of it do not proceed from a bias in our nature, rather than from an original fenfe. Our tafte for fimplicity, which undoubtedly is natural, renders fimple operations more agreeable than what are complex, and confequently makes them appear more natural. It deferves a moft ferious difcuflion, whether the operations of nature be always carried on with the greatest fimplicity, or whether we be not misled by our taste for fimplicity, to be of that opinion.

VOL. II.

intuitively

intuitively certain, that two fubjects, connected with a third by any particular relation, must be connected together by the fame relation. The longest chain of reafoning may be linked together in this manner. Running over fuch a chain, every one of the fubjects must appear intuitively to be connected with that immediately preceding, and with that immediately fubfequent, by the relation affirmed in the propofition; and from the whole united, the propofition, as above mentioned, muft appear intuitively certain. The last step of the process is termed a conclufion, being the last or concluding perception.

No fort of reasoning affords fo clear a notion of the foregoing procefs, as that which is mathematical. Equality is the only mathematical relation; and comparifon therefore is the only means by which mathematical propofitions are ascertained. To that science belong a set of intuitive propofitions, termed axioms, which are all founded on equality. For example: Divide two equal lines, each of them, into a thousand equal parts, a fingle part of the one line must be equal to a single part of the other. Second: Take ten of thefe parts from the one line, and as many from the other, and the remaining parts must be equal: which is more fhortly expreffed thus: From two equal lines take equal parts, and the remainders will be equal; or add equal parts, and the fums will be equal. Third: If two things be, in the fame refpect, equal to a third, the one is equal to the other in the fame refpect. I proceed to fhow the use of these axioms. Two things may be equal without being intuitively fo; which is the cafe of the equality between the three angles of a triangle and two right angles. To demonftrate that truth, it is neceffary to fearch for fome other angles, which appear by intuition to be équal to both. If this property cannot be discovered in any one fet of angles, we must go more leifurely to work, by trying to find angles that are equal to the three angles of a triangle. These being difcovered, we next try to find other angles equal to the

angles