Indian law of evidence | Updated October 2026
Grounds of Opinion, When Relevant: BSA Section 45 and Former Evidence Act Section 51
An opinion is more useful to a court when the reasons, observations and methods behind it can be examined. Section 45 of the Bharatiya Sakshya Adhiniyam, 2023 makes those grounds relevant whenever the opinion of a living person is itself relevant.
Section 45 of the Bharatiya Sakshya Adhiniyam, 2023: Grounds of opinion, when relevant
Statutory provision: Whenever the opinion of any living person is relevant, the grounds on which such opinion is based are also relevant.
Illustration: An expert may give an account of experiments performed by him for the purpose of forming his opinion.
The Bharatiya Sakshya Adhiniyam, 2023 (Act 47 of 2023) came into force on 1 July 2024. Section 45 carries forward the substance of former Section 51 of the Indian Evidence Act, 1872. For matters commenced before the new law took effect, the repeal and savings provision in Section 170 of the BSA should be considered.
What are the grounds of an opinion?
Grounds of opinion are the facts, observations, tests, experience, reasoning or other foundations on which a person forms an opinion. Section 45 permits the court to consider that foundation when the person's opinion is relevant in the first place.
The rule is not confined to scientific experts. It may apply to any living person whose opinion is made relevant by law, including a person with special knowledge of handwriting, customs, usages or relationships. The relevance of an opinion is addressed principally by Sections 39 to 44 of the BSA; Section 45 addresses its supporting grounds.
Relevance does not mean that the court must accept an opinion as correct. The court can consider the reliability of the underlying method, the adequacy of the observations, and the strength of the explanation.
Statutory illustration: Expert experiments
The Act illustrates the rule by allowing an expert to describe experiments performed to form an opinion. For example, if a forensic expert offers an opinion about whether two samples share a common source, the expert may explain the testing procedure, observations and results supporting that conclusion.
The illustration establishes the relevance of the supporting grounds; it does not dispense with other rules governing the proof, authenticity or reliability of the materials used.
Practical applications of Section 45
Medical or scientific expert opinion
When a qualified expert's opinion is relevant under the rules on expert opinions, the tests, examination notes, scientific principles and observations forming the opinion may also be relevant.
Handwriting and signature identification
If an opinion about handwriting is relevant, the witness can explain the samples reviewed, familiarity with the person's writing and the circumstances giving rise to that familiarity. See opinion as to handwriting.
Customary practices and relationships
A person whose opinion about a local custom or family relationship is relevant may describe the particular practices, dealings or conduct on which the opinion rests. Related discussions include general customs and rights and opinions on relationships.
How courts evaluate the grounds of an opinion
- Relevance: Is the underlying opinion relevant under the applicable statutory provision?
- Knowledge: What expertise, experience or special means of knowledge does the witness possess?
- Method: What observations, tests, experiments or records support the conclusion?
- Consistency: Are the grounds internally coherent and consistent with independently established facts?
- Scrutiny: Can the explanation and supporting material be tested through examination and cross-examination?
Where an expert opinion relies on electronic records, the separate rules for electronic evidence, including Sections 61 and 63 of the BSA where applicable, must also be considered. Section 45 alone is not a substitute for proving an electronic record.
Related: facts bearing upon expert opinions.
Historical provision: Section 51 of the Indian Evidence Act, 1872
Section 51 - Grounds of opinion, when relevant: Whenever the opinion of any living person is relevant, the grounds on which such opinion is based are also relevant.
Illustration: An expert may give an account of experiments performed by him for the purpose of forming his opinion.
This earlier wording is retained for readers consulting older judgments, pleadings and evidence-law materials. The current equivalent is Section 45 of the BSA, subject to the applicable commencement and savings rules. For an overview of the former statute, visit the Indian Evidence Act guide.
Official legislation and further reading
- Bharatiya Sakshya Adhiniyam, 2023 - official India Code PDF (see Sections 39-45 and 170).
- India Code - official repository of Indian legislation.
Legislation and its application can depend on the date proceedings commenced and subsequent amendments or judicial decisions. Consult the current official text and obtain professional advice for a specific case.
Frequently asked questions
Which section now governs grounds of opinion?
Section 45 of the Bharatiya Sakshya Adhiniyam, 2023 is the corresponding provision to Section 51 of the Indian Evidence Act, 1872.
Are the reasons for an expert opinion relevant?
Yes. Once the expert's opinion is relevant, its underlying reasons, observations and experiments are also relevant under Section 45.
Does Section 45 make all opinions admissible?
No. The opinion must first be relevant under an applicable legal provision. Section 45 then makes the grounds of that opinion relevant as well.