CERTAINTY, CERTITUDE (Certum, from cerno).— Personal assurance of reality,
possessed in the exercise of immediate knowledge, or attained by the ingathering
of sufficient evidence. Certain knowledge or certainty is the confidence with
which the mind reposes in the information of its faculties. According to the
mode in which it is attained, certainty is immediate by sense and intuition, and
mediate by reasoning and demonstration. Self-consciousness reveals with
certainty the different states and operations of our own minds. We cannot doubt
the reality of what our senses clearly testify. Inference, strictly warranted by
logical law, gives certainty. Reason reveals to us first truths with intuitive
According to the
grounds on which it rests, it is called— Physical, when
it concerns truth which cannot be otherwise, according to the
laws of nature;
Metaphysical, when applied to truth which cannot be otherwise, such as
the first principles of reason; Moral, when it involves
truth expressed in law, which is an imperative of the life.
In connection with the last of the three, popular usage has introduced "moral
certainty" as a condensed expression applicable to conviction resting on moral
evidence in default of direct evidence. In absence of proof of the actual
occurrence, we may have moral evidence founded on the indications of motive on
the part of the agent, and on collateral testimony from a variety of actions.
Moral conviction may amount to the highest degree of probability, and to all
practical purposes may be as influential as certainty. For it should be observed
that probability and certainty are two states of mind, and not two modes of the
reality. The reality is one and the same, but oar knowledge of it may be
probable or certain. Probability has more or less of doubt, and admits of degrees.
doubt, and admits neither of increase nor diminution.
"Certain, in its primary sense, is applied (according to its etymology, from
cerno) to the state of a person's mind; denoting any one's full and complete
conviction; and generally, though not always, implying that there is sufficient
ground for such conviction. It was thence easily transferred metonymically to
the truths or events, respecting which this conviction is rationally
entertained. And uncertain (as well as the substantives and adverbs derived from
these adjectives) follows the same rule. Thus we say, 'It is certain,' &c,
meaning that we are sure; whereas the fact may be uncertain and certain to
different individuals. From not attending to this, the words uncertain and
contingent have been considered as denoting some quality in the things
themselves—and chance has been regarded as a real agent" (Whately,
Logic, app. I.).— V. Locke's Essay, bk. II. ch. VI. and bk.
III. ch. IV.
"The criterion of true knowledge is not to be looked for anywhere abroad without
our own minds, neither in the height above, nor in the depth beneath, but only
in our knowledge and conception themselves " (Cudworth, Eternal and Immutable
Mortality, bk IV. ch. V.).
"The holding of a thing to be true is a phenomenon in our understanding which
may rest on objective grounds, but requires also subjective causes in the mind
of the person judging. If a judgment is valid for every rational being, then its
ground is objectively sufficient, and it is termed a conviction. If, on the
other hand, it has its ground in the particular character of the subject, it is
termed a persuasion" (Kant's Critique of Pure Reason, Transc. Doct. of Method,
ch. II. sec 3; Meiklejohn, 496; Max Müller, II. 703).
As regards the ground of certainty Protagoras and Epicurus in ancient times, and
Hobbes and the modern sensationalists, have made Sense the measure and ground of
certainty. Descartes and his followers founded it on self-consciousness, Cogito
ergo sum; while others have received as certain only what is homologated by
human reason in general.
Certainty is not the peculiar characteristic of knowledge furnished by any one
faculty, but is the common inheritance of any or all of our intellectual
faculties when legitimately exercised within their respective spheres. Though we
are thus naturally and necessarily determined to accept the knowledge furnished
by our faculties, our knowledge, according to Kant, cannot be proved to be
absolute, or a knowledge of things in themselves as they must appear to all
intelligent beings, but is merely relative, or a knowledge of things as they
appear to us. Now, it is true that we cannot, as Kant has expressed it,
objectify the subjective. Without rising out of human nature to the possession
of a higher, we cannot sit in judgment on the faculties of that nature. But,
admitting that our knowledge is relative, we are merely saying it is ours,—it is
human,—it is according to the measure of a man,—it is attained by human
faculties, and must be relative, bearing proportion to the faculties by which it
is attained. We may not know all that can be known of the objects of our
knowledge, but still, what we know, we do know,—we possess a veritable
knowledge. The ground and encouragement of all inquiry is, that our faculties
are fitted to apprehend the reality of things. Faith in their trustworthiness is
spontaneous. Doubt concerning it is an after-thought. Scepticism as a creed is
self-destructive. He who doubts is certain that he doubts. Omnis qui utrum sit
veritas dubitat, in se ipso habet verum, unde non dubitet (Augustine, De vera
Etiam qui negat veritatem esse, concedit veritatem esse; si enim veritas non
est, verum est, veritatem non esse (Thomas Aquinas, Sum. Theol.; S. Descartes,
Method, pt. IV.).— V. EVIDENCE, CRITERION, KNOWLEDGE, PROBABLE.