The means by which the truth or untruth of any relevant fact is established in the trial of an action at law. What is and what is not legal evidence is determined primarily by the pleadings in the action. The early common-law system of pleading was so devised as to narrow down all matters of dispute between the plaintiff and defendant to a single issue of law or fact.

If the issue was one of law, a question was raised for the court only; but if the issue was one of fact, a question was raised for determination by a common-law jury, after a trial in which evidence was introduced on the one side to prove the alleged fact, and on the other to disprove it. The whole system presupposed, on the part of the jury, inability to consider more than one issue of fact at a time, and in the consideration of that one issue, to some extent, lack of capacity to give to different classes of logically relevant evidence their proper weight. It is to the historical development of the jury system, therefore, that many rules of the law of evidence may be attributed, which now seem to be unwarranted in logic and unsuited to the times.

Modern systems of pleading permit the raising of numerous issues of fact, and have thus imposed on the jury duties requiring a higher standard of intelligence than under the ancient system. The rules of evidence, however, partly because they have been found to be practically sufficient, and partly because of the necessity of fixed and definite rules in the branch of the law, have not undergone a corresponding change, and many matters of evidence logically relevant and of considerable probative force are still not legally admissible evidence because of their supposed tendency to 'confuse and mislead the jury.'

1. MUST BE RELEVANT: The rule of first importance in the law of evidence is that it must be relevant in order to be legally admissible. Relevancy depends directly or indirectly on the issue raised by the pleadings. Thus, evidence of a fact may be relevant because it tends directly or indirectly to prove or disprove the fact in issue that is affirmed by one side and denied by the other; or the evidence may be relevant because it tends to prove or disprove some matter of evidence already introduced by the other side for the purpose of proving or disproving the issue raised by the pleadings. But, as has been pointed out, all logically relevant evidence is not legal evidence. Thus evidence which is logically relevant may not be legally admissible because:

(a) Its relevancy is slight or remote. Thus evidence that the defendant was insolvent at a certain time is not admissible to prove that he borrowed money of the plaintiff at that time.

(b) The evidence is of collateral transactions, or (as is sometimes said) res inter alios acta. Thus, in an action to recover damages for negligence it is not permissible to show that the defendant was negligent toward others than the plaintiff, or on trial of a defendant for steal, that he stole from others. The general rule is, however, subject to many limitations and modifications more or less arbitrary. Thus it is permissible to show, in an action of tort, brought to recover for injuries caused by a defective appliance belonging to the defendant, that others were injured by it in a similar manner, and generally, value of land may be shown by proving the selling price of other land similarly situated.

A full consideration of these limitations and modifications is not within the scope of this article. So far, however, as they may be said to rest on any settled principle, their extent now depends upon, whether there is other more available and satisfactory evidence, and to some extent upon the discretion of the trial judge. The character of a party to a civil action is not regarded as relevant, and is, therefore, not the subject of evidence, unless the character is directly put in issue by the pleadings, as in an action for libel. In a criminal trial, however, the defendant may, if he so elects, introduce evidence of his character, which evidence the prosecution may then rebut.

2. HEARSAY. What others than the witness have said before the trial is not generally admissible in evidence because not sworn to, and because not subject to cross-examination. This because not subject to cross-examination. This rule, known as the 'hearsay-evidence rule,' is subject to several important exceptions:

a) Admissions and Confessions:

Statements, either oral or written, made at any time by a party to an action or by his predecessor in interest, may be introduced in evidence against him, but not by him or in his favor. The rule is based upon the inherent probable truth of statements which are prejudicial to the interests of the party making them. Under the rule as to predecessor in interest, the admissions of a deceased person are admissible in evidence in actions against his executor, or admissions as tot he title of real estate made by its then owner are admissible in an action founded upon the title brought against his subsequent grantor. Admissions made by an agent within the scope of his authority are admissible in evidence against the principal. Confessions are strictly admissions made by one charged with a crime, and, because of the necessity of safeguarding one charged with a crime, are not admissible when obtained by means of threats or promises of favor. This rule has been extended by statute in many of the States.

b) Reported Testimony in a Prior Trial:

In general the testimony of a witness in an earlier trial between the same parties and relating to the same issues, or between parties identical in interest with the parties at the present trial, may be introduced in evidence if the witness is dead, insane, unable to attend the trial, out of the jurisdiction, or kept from appearing at the trial by an opposing party. The testimony in the earlier trial must have been sworn to and subject to cross-examination thus obviating the usual objection to hearsay evidence.

C) Dying Declaration:

Declarations made by a person in extremis are admitted in evidence upon the trial of one charged with the crime of homicide, either in favor of the prosecution or the prisoner.

d) Admissions Against Interest:

These should not be confused with admissions. (See above) They are admissions in any form against financial or proprietary interest of the person making them and made by one who, at the time of trial is dead. Unlike admissions, they need not be made by one having some connection with the party to the action. They must, of course, in themselves be relevant to matters in issue at the trial. Thus an endorsement written on a note by the holder that a part of the note is paid, or a book entry that a bill has been paid, or a statement that the declarant is a tenant (rather than the owner), are all admissions against financial or propriety interest, and are admissible in evidence upon proper authentication if relevant, and if the declarant be dead.

e) Book Entries:

Book entries or reports made pursuant to a legal duty or in the usual course of business by one since deceased having personal knowledge of the matter so entered or reported are admissible in evidence to prove the truth of matters contained in the entry. Thus the book entries of clerks or written reports of officers are admissible in evidence under this head, but not the entries in a diary, because not made pursuant to a duty. Closely related to the rule as to entries made in the course of business is the so-called shop-book rule. This rule varies considerably in different jurisdictions, but the effect in all is substantially to allow a party to an action, although present at the trial in person, to prove an account by introducing in evidence his book of account. He is usually required to make preliminary proof that he is engaged in the business in which the charges in the book are made, and that he has made correct entries. A witness may always be allowed to refresh his memory by referring to memoranda or book entries; in that case the memoranda or book entries are, however, not directly in evidence, and the jury may rely only upon the witness's oral testimony.

(f) Res Gestae:

Any statement made at the time of the happening of an event by one who was then present may be introduced when the event itself is in issue or relevant. Such evidence is admitted on the theory that the statement is incidental to the event itself, and to some extent characterizes or explains it. Thus on the murder trial of a defendant it is proper to prove a statement made at the time of the homicide by any person present, which tended to show that the defendant committed the homicide or that the act was intentional or malicious. There are some other exceptions to the hearsay-evidence rule, but these are of infrequent occurrence and of comparative unimportance, and do not admit of discussion here.

III REAL EVIDENCE, WRITINGS:

Legal evidence is not limited to the sworn testimony of witnesses. Specific objects, when properly identified by oral testimony, may often be introduced in evidence when their very existence or their character or appearance tends to prove or disprove an alleged fact. Thus models, parts of machinery, weapons, clothing, etc. may be introduced in evidence. Such evidence cannot of course be submitted to an appellate court as a part of the record of the trial, and for that reason the extent to which such evidence may be received may be limited within the discretion of the court, and in some jurisdictions practically no such evidence is admitted. Writings or documents may generally be introduced directly in evidence for the purpose of proving the truth of statements contained in them. At common law documents purporting to be more than thirty years old required no particular authentication, or, as was said, such documents proved themselves.

The execution of other documents must, however, be proved by the sworn testimony of a witness to the execution, or, if he be dead, by proof of the handwriting of the person who executed the document. The so-called best-evidence rule applies to documentary evidence. Briefly stated, it is that the best evidence of the contents of a document is the document itself, and that no other evidence of the contents of a written instrument is admissible. This rule is subject to many exceptions, real or apparent. Thus:

(a) Where the original document is in duplicate form any one of the duplicates may be introduced in evidence as an original.

(b) Secondary evidence (i.e.a copy or oral testimony) of a written notice is admissible.

(c) Matters of public record may be proven by secondary evidence, in most jurisdictions by a certified copy of the record.

(d) Secondary evidence may also be introduced to prove an instrument which has been lost or destroyed, or whenever the other party to an action, having the document in his possession, fails to produce it at the trial for the purpose of preventing its being introduced in evidence on due notice. One who has willfully destroyed a document will not, however, be allowed to give evidence of its contents. When proof of a document is offered but for the purpose of proving the truth or untruth of any statement contained in it, it is real evidence, as distinguished from a writing; and the best-evidence rule should and probably does not apply. The common-law rule as to proof of documents has been much modified by statute. In most jurisdictions all documents attested before a notary or corresponding officer are prima facie admissible in evidence if relevant.