Violent and necessary, 2. Probable, 3. and lastly, Slight and rash.[46]
But finding that this head of Presumptive Evidence (which makes so large
a part with them and with us in the trial of all causes, and
particularly criminal causes) is extremely difficult to ascertain,
either with regard to what shall be considered as exclusively creating
any of these three degrees of presumption, or what facts, and how
proved, and what marks and tokens, may serve to establish them, even
those Civilians whose character it is to be subtle to a fault have been
obliged to abandon the task, and have fairly confessed that the labors
of writers to fix rules for these matters have been vain and fruitless.
One of the most able of them[47] has said, "that the doctors of the law
have written nothing of value concerning presumptions; nor is the
subject-matter such as to be reduced within the prescribed limit of any
certain rules. In truth, it is from the actual existing case, and from
the circumstances of the persons and of the business, that we ought
(under the guidance of an incorrupt judgment of the mind, which is
called an equitable discretion) to determine what presumptions or
conjectural proofs are to be admitted as rational or rejected as false,
or on which the understanding can pronounce nothing, either the one way
or the other."

It is certain, that, whatever over-strictness is to be found in the
older writers on this law with regard to evidence, it chiefly related to
the mere competency of witnesses; yet even here the rigor of the Roman
lawyers relaxed on the necessity of the case. Persons who kept houses of
ill-fame were with them incompetent witnesses; yet among the maxims of
that law the rule is well known of _Testes lupanares in re lupanari_.

In ordinary cases, they require two witnesses to prove a fact; and
therefore they held, "that, if there be but one witness, and no probable