1. Conclusive proof—in other words, raise a conclusive presumption;
2. Presumptive proof—in other words, raise a conditional or rebuttable presumption;
3. Insufficient evidence—that is to say, do not amount to proof, and raise no presumption, conclusive or conditional;
4. Exclusive evidence—that is to say, are the only facts which in respect of the matter in issue possess any probative force at all;
5. No evidence—that is to say, are destitute of evidential value.
I. Conclusive presumptions.—By conclusive proof is meant a fact possessing probative force of such strength as not to admit of effective contradiction. In other words, this fact amounts to proof irrespective of the existence or non-existence of any other facts whatsoever which may possess probative force in the contrary direction. By a conclusive presumption is meant the acceptance or recognition of a fact by the law as conclusive proof.
Presumptive or conditional proof, on the other hand, is a fact which amounts to proof, only so long as there exists no other fact amounting to disproof. It is a provisional proof, valid until overthrown by contrary proof. A conditional or rebuttable presumption is the acceptance of a fact by the law as conditional proof.[[476]]
One of the most singular features in early systems of procedure is the extent to which the process of proof is dominated by conclusive presumptions. The chief part of the early law of evidence consists of rules determining the species of proof which is necessary and sufficient in different cases, and allotting the benefit or burden of such proof between the parties. He who would establish his case must maintain it, for example, by success in that judicial battle the issue of which was held to be the judgment of Heaven (judicium Dei); or he must go unscathed through the ordeal, and so make manifest his truth or innocence; or he must procure twelve men to swear in set form that they believe his testimony to be true; or it may be sufficient if he himself makes solemn oath that his cause is just. If he succeeds in performing the conditions so laid upon him, he will have judgment; if he fails even in the slightest point, he is defeated. His task is to satisfy the requirements of the law, not to convince the court of the truth of his case. What the court thinks of the matter is nothing to the point. The whole procedure seems designed to take away from the tribunals the responsibility of investigating the truth, and to cast this burden upon providence or fate. Only gradually and reluctantly did our law attain to the conclusion that there is no such royal road in the administration of justice, that the heavens are silent, that the battle goes to the strong, that oaths are naught, and that there is no just substitute for the laborious investigation of the truth of things at the mouths of parties and witnesses.
The days are long since past in which conclusive presumptions played any great part in the administration of justice. They have not, however, altogether lost their early importance. They are, indeed, almost necessarily more or less false, for it is seldom possible in the subject-matter of judicial procedure to lay down with truth a general principle that any one thing is conclusive proof of the existence of any other. Nevertheless such principles may be just and useful even though not wholly true. We have already seen how they are often merely the procedural equivalents of substantive rules which may have independent validity. They have also been of use in developing and modifying by way of legal fictions the narrow and perverted principles of the early law. As an illustration of their employment in modern law we may cite the maxim Res judicata pro veritate accipitur. A judgment is conclusive evidence as between the parties, and sometimes as against all the world, of the matters adjudicated upon. The courts of justice may make mistakes, but no one will be heard to say so. For their function is to terminate disputes, and their decisions must be accepted as final and beyond question.
II. Conditional presumptions.—The second class of rules for the determination of probative force are those which establish rebuttable presumptions. For example, a person shown not to have been heard of for seven years by those who would naturally have heard of him if he had been alive, is presumed to be dead. So also a negotiable instrument is presumed to have been given for value. So also a person accused of any offence is presumed to be innocent.