Between the commission of an offence and its proof in a court of justice there lies a wide field for the exercise or perversion of human ingenuity. The subject of evidence is one which has taxed man’s reasoning powers to the utmost; and the subtle distinctions of the Roman law, with its probatio, præsumptio juris, præsumptio juris tantum: the endless refinements of the glossators, rating evidence in its different grades, as probatio optima, evidentissima, apertissima, legitima, sufficiens, indubitata, dilucida, liquida, evidens, perspicua, and semiplena; and the artificial rules of the common law, so repugnant frequently to human common sense, all alike show the importance of the subject, and its supreme difficulty. The semi-barbarian, impatient of such expenditure of logic, arrived at results by a shorter process.
The time has passed for the romantic school of writers who assume that the unsupported oath of the accused was originally sufficient to clear him of a charge, when the fierce warrior disdained to shrink from the consequences of his act. It was not, indeed, until long after the Teutonic tribes had declined from the assumed virtues of their native forests, that an unsupported oath was receivable as evidence, and the introduction of such a custom may be traced to the influence of the Roman law, in which the importance of the oath was overwhelming.[28] The Wisigoths, who moulded their laws on the Roman jurisprudence, were the only race of barbarians who permitted the accused, in the absence of definite testimony, to escape on his single oath,[29] and this exception only tends to prove the rule, for at the council of Valence, in 855, the Wisigothic custom was denounced in the strongest terms as an incentive to perjury.[30] It is true that the oath of a master could clear a slave accused of certain crimes,[31] which was no less an incentive to perjury, for the master was liable in case of conviction, but presumably in such case he took upon himself the responsibility and laid himself open to an accusation of perjury. As a rule, however, we may assume that the purgatorial power of a single oath was an innovation introduced by the church, which was trained in the Roman institutions and claimed for its members the privilege, when testimony was deficient, of clearing themselves by appealing in this manner to God.[32] Continued contact with the remains of Roman civilization strengthened the custom, and its development was to a great extent due to the revival of the study of the imperial jurisprudence in the twelfth century.[33] The primitive principle is well expressed in the Frisian code, where the pleader says, “I swear alone, if thou darest, deny my oath and fight me,”[34] where the oath is only the preliminary to proof by the judgment of God.
The exceptions to this in the early legislation of the barbarians are merely special immunities bestowed on rank. Thus in one of the most primitive of the Anglo-Saxon codes, which dates from the seventh century, the king and the bishop are permitted to rebut an accusation with their simple asseveration, and the thane and the mass-priest with a simple oath, while the great body both of clerks and laymen are forced to clear themselves by undergoing the regular form of canonical compurgation which will be hereafter described.[35] So, in the Welsh legislation, exemption from the oath of absolution was accorded to bishops, lords, the deaf, the dumb, men of a different language, and pregnant women.[36] Instances of class-privileges such as these may be traced throughout the whole period of the dark ages, and prove nothing except the advantages claimed and enjoyed by caste. Thus, by the law of Southern Germany, the unsupported oath of a claimant was sufficient, if he were a person of substance and repute, while, if otherwise, he was obliged to provide two conjurators,[37] and in Castile, the fijodalgo, or noble, could rebut a claim in civil cases by taking three solemn oaths, in which he invoked on himself the vengeance of God in this world and the next.[38]
So far, indeed, were the Barbarians from reposing implicit confidence in the integrity of their fellows that their earliest records show how fully they shared in the common desire of mankind to place the oath under the most efficient guarantees that ingenuity could devise. In its most simple form the oath is an invocation of some deity or supernatural power to grant or withhold his favor in accordance with the veracity of the swearer, but at all times men have sought to render this more impressive by interposing material objects dear to the individual, which were understood to be offered as pledges or victims for the divine wrath. Thus, among the Hindus, the ancient Manava Dharma Sastra prescribes the oath as satisfactory evidence in default of evidence, but requires it to be duly reinforced—
“In cases where there is no testimony, and the judge cannot decide upon which side lies the truth, he can determine it fully by administering the oath.
“Oaths were sworn by the seven Maharshis, and by the gods, to make doubtful things manifest, and even Vasishtha sware an oath before the king Sudama, son of Piyavana, when Viswamitra accused him of eating a hundred children.
“Let not the wise man take an oath in vain, even for things of little weight; for he who takes an oath in vain is lost in this world and the next.
“Let the judge swear the Brahman by his truth; the Kshatriya by his horses, his elephants, or his arms; the Vaisya by his cows, his corn, and his gold; the Sudra by all crimes.”[39]
And in the more detailed code of Vishnu there is an exceedingly complicated system of objects to be sworn upon, varying with the amount at stake and the caste of the swearer.[40]
We see the same custom in Greece, where Homer represents Hera as exculpating herself by an oath on the sacred head of Zeus, and on their marriage-bed, a practice which mortals imitated by swearing on the heads of their children, or on that of their patron, or of the king.[41] Under the Roman law, oaths were frequently taken on the head of the litigant, or on those of his children.[42] The Norse warrior was sworn, like the Hindu Kshatriya, on his warlike gear:
“Oaths shalt thou
First to me swear,
By board of ship,