Opinions of third persons: experts, handwriting, the Examiner of Electronic Evidence, custom and relationship (sections 39 to 45)

1. Section 39: opinions of experts

When the Court has to form an opinion on a point of foreign law, science or art, or any other field, or as to identity of handwriting or finger impressions, the opinions of persons specially skilled in it are relevant, and such persons are called experts. "Or any other field" is new: the 1872 text said only "science or art". It widens the section to experts in disciplines such as accountancy, ballistics, digital forensics and valuation without any argument about whether they are "science".

Who is an expert. A person with special skill, acquired by study or experience, in the field in question. Formal qualifications help but are not decisive; experience may be enough. The party calling the witness must first establish his expertise. The illustrations: the symptoms of a poison, whether symptoms show unsoundness of mind (relevant to section 22 BNS, the insanity defence), and whether two documents were written by the same hand.

Section 39(2): when the Court has to form an opinion on any matter relating to information transmitted or stored in a computer resource or other electronic or digital form, the opinion of the Examiner of Electronic Evidence referred to in section 79A of the Information Technology Act, 2000 is a relevant fact; the Explanation declares him an expert. Under section 79A of the IT Act, the Central Government notifies departments, bodies or agencies as Examiners of Electronic Evidence.

2. Weight of expert evidence

An expert's opinion is advisory. The Court must form its own judgment on the materials, and the expert's reasons are as important as his conclusion. Section 45 (old s.51) makes the grounds of an opinion relevant, so an expert may describe the experiments he performed.

• State of Himachal Pradesh v. Jai Lal, 1999 INSC 393, (1999) 7 SCC 280. An expert's function is to give the Court the scientific criteria for testing his conclusions, so that the Court can form an independent judgment. An opinion without reasons has little value.
• Ramesh Chandra Agrawal v. Regency Hospital Ltd., 2009 INSC 1131, (2009) 9 SCC 709. The real function of the expert is to put before the Court all the materials with reasons; the Court is not bound by his view.
• Medical evidence and eye-witnesses. Where reliable eye-witness evidence conflicts with medical opinion, the eye-witness evidence is ordinarily preferred, unless the medical evidence rules out the prosecution version altogether.

3. Handwriting: two routes

Handwriting expert (section 39). Handwriting identification is regarded as an imperfect science, and the earlier view was that a conviction should not rest on it without corroboration: Magan Bihari Lal v. State of Punjab, 1977 INSC 57, (1977) 2 SCC 210. In Murari Lal v. State of Madhya Pradesh, 1979 INSC 248, (1980) 1 SCC 704, the Court clarified that there is no rule of law requiring corroboration. It is a rule of caution. If, after testing the expert's reasons, the Court is fully satisfied, it may act on his opinion alone.

Person acquainted with the handwriting (section 41(1), old s.47). A non-expert may give his opinion if he is acquainted with the handwriting: he has seen the person write, or has received documents written by him in reply to his own, or such documents have been habitually submitted to him in the ordinary course of business. Illustration: B, a merchant who corresponds with A, B's clerk who files the letters, and B's broker who advises on them can all give an opinion, though none has seen A write.

The Court itself may compare a disputed writing, signature, seal or finger impression with an admitted one, and may direct a person in court to write for comparison (section 72, old s.73), though it should be slow to decide on its own comparison without expert help.

Electronic signature (section 41(2), old s.47A). The opinion of the Certifying Authority which issued the Electronic Signature Certificate is relevant.

4. Facts bearing on expert opinion: section 40

Facts not otherwise relevant become relevant if they support or are inconsistent with an expert opinion (old s.46). That other persons poisoned by the same substance showed the symptoms the expert describes, or that similar harbours without the sea-wall also silted up, are the illustrations.

5. Custom, usages and relationship

• Section 42 (old s.48): on the existence of a general custom or right (one common to a considerable class of persons), the opinions of persons likely to know of it are relevant. The right of villagers to use a particular well.
• Section 43 (old s.49): on the usages and tenets of a body of men or family, the constitution and governance of a religious or charitable foundation, or the meaning of words used in particular districts or by particular classes, opinions of persons with special means of knowledge are relevant.
• Section 44 (old s.50): on the relationship of one person to another, the opinion, expressed by conduct, of a person who as a family member or otherwise has special means of knowledge, is relevant. The proviso: such opinion is not sufficient to prove a marriage in proceedings under the Divorce Act, 1869, or in prosecutions for bigamy and related offences under sections 82 and 84 BNS.

6. Problem

The question is whether A was the legitimate son of B. Is the fact that A was always treated as such by the members of the family relevant? (June 2025)

Conclusion. Yes. This is illustration (b) to section 44. The family's conduct in treating A as B's legitimate son is their opinion, expressed by conduct, on a relationship of which they have special means of knowledge. It is relevant, though it is evidence to be weighed, not conclusive. If the question were whether A's parents were validly married in a bigamy prosecution under section 82 BNS, such conduct alone would not be sufficient (proviso). The same family could also have their statements proved under section 26(e) if they were dead and spoke before the dispute arose.

How this is examined

"Expert opinion" is a regular six-mark note (Feb 2025, Law of Evidence June 2025). For ten marks the question asks who is an expert and the evidentiary value of expert opinion. Cover section 39 with "any other field" and section 39(2), the weight cases (Jai Lal, Murari Lal), the two handwriting routes, and a paragraph on sections 42 to 44. The legitimacy problem on section 44 has appeared as a Unit II problem.