BSA Section 45: Grounds of Opinion, When Relevant (Evidence Act 51 Mapping) (2026)
What Section 45 of the Bharatiya Sakshya Adhiniyam (BSA) does: when a person's opinion is relevant, the grounds on which that opinion is based are also relevant. It carries forward Section 51 of the old Indian Evidence Act. Last verified October 2026.
Explainer · Evidence Law · BSA
Section 45 of the Bharatiya Sakshya Adhiniyam (BSA), the new evidence law in force since 1 July 2024, provides that when a person's opinion is relevant, the grounds behind that opinion are relevant too. It carries forward Section 51 of the Indian Evidence Act. If you are looking up "Section 45" expecting the expert opinion rule, note the numbers have moved: expert opinion is now Section 39 of the BSA, not Section 45. This explainer sets out what Section 45 actually covers, why it matters, and how it maps to the old law. Last verified October 2026.
- What it is: Section 45 of the BSA makes the grounds of a relevant opinion also relevant, so the court can test how the opinion was reached.
- Old section: it carries forward Section 51 of the Indian Evidence Act, 1872.
- Not expert opinion: the expert opinion rule, which was old Section 45, is now Section 39 of the BSA.
- How it is used: an expert may explain the experiments, tests or data behind an opinion, and those grounds come in as evidence.
01A common point of confusion
Under the old Indian Evidence Act, "Section 45" was the famous expert opinion rule. Since 1 July 2024 the Evidence Act is replaced by the BSA, and the opinion sections were renumbered. Expert opinion is now Section 39 of the BSA. Section 45 of the BSA carries a different, closely linked rule: that the grounds on which a relevant opinion rests are themselves relevant. That rule was Section 51 of the old Act.
This matters when you cite or search. A proceeding on or after 1 July 2024 uses the BSA number. An older matter keeps the Evidence Act number. Read each by the date of the proceeding.
02What Section 45 says
Section 45 of the BSA provides that whenever the opinion of any living person is relevant, the grounds on which such opinion is based are also relevant.
The idea in one line
An opinion does not stand alone. The reasoning and the material the opinion rests on come in with it, so the court can test the opinion rather than accept it blindly.
The illustration makes the point: an expert may give an account of experiments which he performed for the purpose of forming his opinion. So a handwriting expert can explain the comparison method used, and a medical witness can explain the findings that led to a conclusion. The grounds are admitted along with the opinion.
03Why the grounds matter
The value of an opinion depends on its basis. A bare conclusion, with nothing to support it, carries little weight. Section 45 lets the party leading the opinion bring out the reasons, tests and data behind it, and lets the other side cross-examine on those grounds.
This is why courts repeatedly say that expert opinion is weak if the expert does not explain the process. Section 45 is the provision that makes those grounds admissible. It works hand in hand with the opinion sections, including expert opinion under Section 39 of the BSA.
04Old to new: Evidence Act 51 to BSA 45
Section 51 of the Indian Evidence Act is now Section 45 of the BSA. The wording and the illustration are carried over, so the doctrine is unchanged.
| Point | Old law (Indian Evidence Act) | New law (BSA) |
|---|---|---|
| Opinion of experts | Section 45 | Section 39 |
| Grounds of opinion | Section 51 | Section 45 |
| Court may presume certain facts | Section 114 | Section 119 |
Because the text is carried over, judgments decided under Section 51 of the Evidence Act continue to guide how Section 45 of the BSA is read.
05What changed
The substance did not change. The rule that the grounds of a relevant opinion come in with the opinion is carried over, along with the illustration. The change is the section number and the modern drafting.
One practical note: this is an evidence provision, so it has no punishment, and no cognizable, bailable or triable status of its own. Those attributes belong to the offence being tried. Section 45 simply helps the court weigh an opinion by looking at what it rests on.
06Where Claw fits
Claw is an all-in-one legaltech platform for Indian advocates, law firms, and corporate legal teams, combining AI-based case search, an AI legal assistant (Legal GPT), case management, and compliance automation across all Indian courts and tribunals.
What an opinion is worth often depends on how a court has treated similar grounds, whether for a handwriting, medical, forensic or technical expert. Claw lets you look that up across more than 30 crore judgments with results in under 5 seconds, and lets you follow a live matter, with its orders and hearings, by party or advocate name across 9,102 courts, benches and forums. Reported authority runs from Supreme Court rulings of 1950 and High Court rulings of 1990 to the latest orders.
Claw does not use the documents you upload to train its AI models. Create a free Claw account to see how Section 45 of the BSA, and Section 51 of the old Act, have been applied to the grounds of an opinion, and to track a pending matter. To search the wider body of law, see case search across Indian courts.
07Sources and further reading
- India Code (official text of the BSA, 2023): indiacode.nic.in
- PRS Legislative Research (BSA overview and comparison): prsindia.org
- Section 45, BSA (bare text): advocatekhoj.com
- Claw: clawlaw.in
This explainer is general information, not legal advice. The law changes through amendments and judgments, so check the current text and take advice from counsel before you act.
08Frequently asked questions
What is Section 45 of the BSA?
Section 45 of the Bharatiya Sakshya Adhiniyam, 2023 provides that whenever the opinion of any living person is relevant, the grounds on which that opinion is based are also relevant. It restates Section 51 of the old Indian Evidence Act.
Is Section 45 the expert opinion rule?
No. Under the BSA, expert opinion is Section 39. Section 45 deals with the grounds of a relevant opinion. The old Evidence Act Section 45 on experts has moved to Section 39, so the numbers do not line up.
Why are the grounds of an opinion relevant?
Because an opinion is only as good as its basis. Admitting the reasons, tests and data behind the opinion lets the court weigh it properly and lets the other side cross-examine on those grounds.
Is Section 45 an offence with a punishment?
No. It is a rule of evidence about relevancy. It has no punishment or cognizable, bailable or triable status of its own. Those belong to the offence being tried in the matter.
Does old case law on Section 51 still apply?
Yes, in large part. Because the wording and the illustration are carried over, judgments decided under Section 51 of the Evidence Act still guide how Section 45 of the BSA is read.
Can I find judgments on expert grounds in Claw?
Yes. Claw lets you search more than 30 crore judgments on the grounds of an opinion under Section 45 or the old Section 51, by party or advocate, with results in under 5 seconds, and track orders and hearings across 9,102 courts, benches and forums. It researches and tracks the matter but does not give legal advice.