A fact is said to be logically relevant to another when it bears such a causal relation with the other as to render probable the existence or non-existence of the latter. As stated above, all facts which are logically relevant are not legally relevant. One fact is said to be legally relevant to another, only when the one is connected with the other in any of the ways referred to in Ss. 5 to 55 of the Evidence Act.
Logical relevancy is wider than legal relevancy; every fact which is legally relevant is logically relevant, but every fact which is logically relevant is not necessarily legally relevant. Thus, a confession made to a police officer may appear to be logically relevant, but such a confession is not legally relevant, for S. 25 of the Act declares that it cannot be used as evidence against the person making it. The Indian Evidence Act lays down, in Ss. 5-55, what facts are relevant; but the mere fact of logical relevancy does not ensure the admissibility of a fact.
Very often, public considerations of fairness and the practical necessity for reaching speedy decisions necessarily cause the rejection of much of the evidence which may be logically relevant. Thus, all evidence that is admissible is relevant, but all that is relevant is not necessarily admissible. Relevancy is the genus of which admissibility is a species. Thus, oral statements which are hearsay may be relevant, but not being direct evidence, are not admissible. Legal relevancy is, for the most part, based upon logical relevancy, but it is not correct to say that all that is logically relevant is necessarily legally relevant and vice versa. Certain classes of facts which, in ordinary life, are relied upon as logically relevant are rejected by law as legally irrelevant. Cases of exclusion of logically relevant facts by positive rules of law are: (i) Exclusion of oral by documentary evidence: Ss. 91-99.
(ii) Exclusion of evidence of facts by estoppel: Ss. 115-117. (iii) Exclusion of privileged communications, such as confidential communications with a legal adviser, communication during marriage, official communications, etc.
: Ss. 121-130