r a cardinal deacon of the Roman Church,
unless there be twenty-seven witnesses; nor a subdeacon, an acolyte,
an exorcist, a reader or a doorkeeper without seven witnesses." Now
the sin of one who is of higher dignity is more grievous, and
consequently should be treated more severely. Therefore neither is
the evidence of two or three witnesses sufficient for the
condemnation of other persons.

_On the contrary,_ It is written (Deut. 17:6): "By the mouth of two
or three witnesses shall he die that is to be slain," and further on
(Deut. 19:15): "In the mouth of two or three witnesses every word
shall stand."

_I answer that,_ According to the Philosopher (Ethic. i, 3), "we must
not expect to find certitude equally in every matter." For in human
acts, on which judgments are passed and evidence required, it is
impossible to have demonstrative certitude, because they are about
things contingent and variable. Hence the certitude of probability
suffices, such as may reach the truth in the greater number of cases,
although it fail in the minority. Now it is probable that the
assertion of several witnesses contains the truth rather than the
assertion of one: and since the accused is the only one who denies,
while several witness affirm the same as the prosecutor, it is
reasonably established both by Divine and by human law, that the
assertion of several witnesses should be upheld. Now all multitude is
comprised of three elements, the beginning, the middle and the end.
Wherefore, according to the Philosopher (De Coelo i, 1), "we reckon
'all' and 'whole' to consist of three parts." Now we have a triple
voucher when two agree with the prosecutor: hence two witnesses are
required; or for the sake of greater certitude three, which is the
perfect number. Wherefore it is written (Eccles. 4:12): "A threefold
cord is not easily broken": and Augustine, commenting on John 8:17,
"The testimony of two men is true," says (Tract. xxxvi) that "there
is here a mystery by which we are given to understand that Trinity
wherein is perpetual stability of truth."

Reply Obj. 1: No matter how great a number of witnesses may be
determined, the evidence might sometimes be unjust, since is written
(Ex. 23:2): "Thou shalt not follow the multitude to do evil." And yet
the fact that in so many it is not possible to have certitude without
fear of error, is no reason why we should reject the certitude which
can probably be had through two or three witnesse