Duties of Experts to the Court

1. Introduction

An expert witness is a person possessing specialised knowledge, skill, experience, training or education in a particular field, whose opinion assists the court in deciding matters that fall outside ordinary judicial or common knowledge.

Under the Bharatiya Sakshya Adhiniyam, 2023 (BSA), the principal provision is Section 39, which deals with opinions of experts. It covers opinions relating to foreign law, science, art, any other specialised field, handwriting, fingerprints and, importantly, electronic or digital evidence through the Examiner of Electronic Evidence. Sections 40 and 45 further deal with facts bearing upon expert opinions and the grounds of opinions.

The BSA substantially carries forward the principles previously contained in Sections 45–51 of the Indian Evidence Act, 1872. Therefore, the extensive Supreme Court jurisprudence developed under the old Evidence Act remains highly relevant in understanding the duties and evidentiary value of experts.

The fundamental principle is:

An expert is an assistant to the court, not an advocate for either party.

The expert's primary obligation is to assist the court impartially by presenting the relevant scientific or specialised material, methodology, reasoning and limitations, leaving the ultimate determination to the judge.

2. Meaning of an Expert Witness

Section 39 BSA makes an expert opinion relevant where the court has to form an opinion concerning:

• foreign law;
• science;
• art;
• any other specialised field;
• handwriting;
• fingerprints; and
• electronic or digital information, through the legally recognised Examiner of Electronic Evidence. 

An individual does not become an expert merely because he or she has a professional title.

The person must possess special knowledge, skill, study, training or experience sufficient to assist the court.

In State of H.P. v. Jai Lal, (1999) 7 SCC 280, the Supreme Court explained that an expert must have made the relevant subject a matter of particular study, practice or observation and must possess special knowledge of it.

3. The Central Duty: Assistance to the Court

The most important duty of an expert is to assist the court rather than advance the case of the party who called him.

An expert must place before the court:

1. the relevant scientific or technical material;
2. the facts and data examined;
3. the methodology employed;
4. the assumptions made;
5. the reasoning connecting the data to the conclusion;
6. the limitations of the methodology; and
7. the conclusion that reasonably follows from the material.

The expert should enable the judge, who may not possess specialised knowledge, to independently evaluate the issue.

This principle was authoritatively stated in State of H.P. v. Jai Lal. The Supreme Court described expert evidence as essentially advisory and held that the expert's duty is to provide the scientific criteria by which the judge can test the accuracy of the conclusion.

Thus, the expert does not decide the case.

Example

A forensic expert may say:

"The DNA profiles obtained from Samples A and B are consistent with originating from the same individual, subject to the stated statistical limitations."

The expert should not ordinarily transform this scientific conclusion into:

"Therefore, the accused is guilty."

The first is expert assistance; the second attempts to usurp the judicial function.

4. Duty of Impartiality

The expert must remain independent and objective.

The fact that an expert has been engaged or called by one party does not make the expert a partisan witness.

The expert should not:

• tailor the opinion to the client's desired result;
• suppress unfavourable scientific material;
• ignore contradictory evidence;
• exaggerate the certainty of a conclusion;
• selectively rely upon favourable data;
• present advocacy as scientific opinion; or
• deliberately create a misleading impression.

The expert's loyalty is ultimately to the truth-finding function of the court.

This is particularly important in civil litigation, medical negligence cases, intellectual-property disputes, tax matters, construction disputes, valuation cases and criminal trials involving forensic science.

5. Duty to Possess Appropriate Expertise

An expert should testify only within the area in which he or she possesses appropriate expertise.

For example:

• a cardiologist should not ordinarily give an authoritative opinion on forensic toxicology merely because both are medical disciplines;
• a handwriting expert should not give an opinion on DNA analysis;
• a computer-security expert should not automatically be treated as an expert in every aspect of digital forensics.

In State of H.P. v. Jai Lal, the Supreme Court stressed that special study, practice, observation or experience in the particular subject is necessary to qualify a person as an expert.

Practical rule

Expertise must correspond to the question being placed before the court.

6. Duty to State the Basis of the Opinion

An expert cannot simply announce a conclusion.

The opinion should disclose the basis on which it has been reached.

This is one of the most important principles governing expert evidence.

The Supreme Court repeatedly emphasises that the evidentiary value of an expert's opinion depends heavily upon:

• the underlying data;
• the reasoning process;
• the methodology;
• the expert's competence; and
• the connection between the facts examined and the conclusion.

In Ramesh Chandra Agrawal v. Regency Hospital Ltd., (2009) 9 SCC 709, the Supreme Court emphasised that the credibility of expert evidence depends upon the reasons supporting the conclusion and the data and material upon which the conclusion is based. Mere assertion without supporting data may provide little or no assistance to the court.

7. Duty to Explain the Methodology

An expert should explain how the conclusion was reached.

For scientific evidence, the court should be able to understand:

• what material was examined;
• what tests were performed;
• what methodology was used;
• whether the methodology is accepted or recognised;
• what assumptions were made;
• whether alternative explanations were considered; and
• what limitations affect the conclusion.

This enables the court to distinguish a genuine scientific opinion from an unsupported assertion.

8. Duty to Put Relevant Material Before the Court

An expert should provide the court with the relevant material necessary for independent assessment.

The expert should not merely state:

"In my opinion, X is correct."

Instead, the expert should explain:

"I reach this conclusion because A, B and C were observed, the applicable methodology produced D, and the alternative explanation E was considered but rejected for reasons F and G."

This enables the court to assess the reliability of the opinion.

The Supreme Court's decision in Dayal Singh v. State of Uttaranchal, (2012) 8 SCC 263 is particularly important. The Court held that if an expert does not disclose the material, similarities, dissimilarities or other factors that influenced the conclusion, the expert fails in the duty to take the court into confidence.

9. Duty Not to Give an Ipse Dixit Opinion

An ipse dixit opinion is essentially a conclusion supported by nothing more than the expert's own assertion.

Courts are not required to accept:

"I am an expert, therefore my opinion must be correct."

The expert must provide reasons capable of evaluation.

In Dayal Singh, the Supreme Court specifically rejected reliance upon the mere ipse dixit of an expert and emphasised that the value of expert evidence lies substantially in the cogency of the reasons supporting the conclusion.

Therefore:

Expertise + reasoning + supporting material = meaningful expert evidence.

Expertise without reasoning = weak evidence.

10. Duty to Maintain Scientific Objectivity

An expert must distinguish between:

• established scientific propositions;
• reasonable professional opinion;
• disputed scientific propositions;
• assumptions; and
• matters of uncertainty.

The expert should not present a disputed proposition as an absolute scientific fact.

Where scientific uncertainty exists, it should be disclosed.

For example, an expert should be willing to state:

"The available evidence supports conclusion A more strongly than conclusion B, but the evidence does not permit absolute certainty."

Such qualification is a sign of scientific reliability rather than weakness.

11. Duty to Consider Contrary Evidence

An expert should not deliberately ignore evidence that contradicts his opinion.

If material evidence points in another direction, the expert should:

1. identify it;
2. explain its significance;
3. state why it does or does not alter the conclusion.

This is especially important where opposing experts have reached different conclusions.

A court must be able to see why one scientific interpretation is stronger than another.

12. Duty to Assist, Not Decide

One of the clearest principles in Indian law is that an expert must not assume the role of the judge.

In State (Delhi Administration) v. Pali Ram, (1979) 2 SCC 158, concerning handwriting evidence, the Supreme Court explained that the real function of an expert is to put before the court the relevant material and reasons so that the court can form its own judgment. The expert is not to decide questions that ultimately belong to the court.

Thus, an expert can assist the court on:

"Whether the handwriting contains characteristics consistent with the specimen."

But the ultimate legal finding:

"The accused forged the document."

belongs to the court.

13. Duty to Remain Within the Scope of Expertise

Experts should not exceed the limits of their specialised knowledge.

Suppose a forensic pathologist establishes the likely cause and manner of death. That does not automatically authorise the expert to determine:

• who committed the offence;
• whether the accused had criminal intention;
• whether the prosecution witnesses are truthful; or
• whether the accused is legally guilty.

Those are judicial questions.

14. Duty to Face Cross-Examination

An expert should be prepared to defend the methodology and reasoning underlying the opinion.

Under the traditional framework, an expert report does not automatically become conclusive evidence merely because it has been prepared by a qualified person.

In State of H.P. v. Jai Lal, the Supreme Court stressed that the expert's report does not automatically become evidence merely upon submission; the expert may be required to be examined and subjected to cross-examination.

Cross-examination allows the opposing party to test:

• qualifications;
• assumptions;
• methodology;
• factual foundation;
• errors;
• omissions;
• alternative explanations;
• scientific literature; and
• possible bias.

15. Duty to Correct Errors

If an expert discovers that an earlier opinion was based on:

• incorrect data;
• defective methodology;
• incomplete information;
• computational error;
• mistaken assumption; or
• subsequently discovered material,

the expert should correct or qualify the opinion.

The duty to the court is more important than protecting one's professional reputation.

An expert should not defend a conclusion merely because it has already been expressed.

16. Duty Regarding Electronic and Digital Evidence

The BSA expressly expands the statutory framework to modern evidence.

Section 39(2) provides that where the court has to form an opinion concerning information transmitted or stored in a computer resource or another electronic/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 duty of a digital expert consequently includes careful attention to:

• integrity of electronic evidence;
• acquisition methodology;
• preservation;
• metadata;
• chain of custody;
• forensic imaging;
• authentication;
• hash values where applicable;
• possibility of alteration;
• limitations of the extraction process; and
• reproducibility of the analysis.

A digital expert should clearly distinguish between:

what the electronic evidence actually establishes and what the expert merely infers from it.

17. Duty to Maintain Records and Working Material

A responsible expert should maintain adequate records of:

• documents examined;
• samples received;
• tests conducted;
• laboratory procedures;
• calculations;
• photographs;
• measurements;
• software or instruments used;
• relevant literature;
• assumptions;
• intermediate findings; and
• final conclusions.

These records permit the opposing party and the court to test the reliability of the opinion.

18. Duty to Disclose Limitations

No scientific technique is necessarily infallible.

Therefore, an expert should disclose relevant limitations.

For example:

• inadequate sample size;
• contamination;
• degraded biological material;
• incomplete medical records;
• poor-quality images;
• insufficient comparison material;
• unreliable assumptions;
• limitations in statistical significance; or
• methodological constraints.

A candid disclosure of limitations increases the reliability of expert evidence.

19. Duty When Experts Disagree

Different experts may legitimately reach different conclusions.

The existence of disagreement does not automatically mean that one expert is dishonest.

The court must evaluate:

• qualifications;
• experience;
• methodology;
• underlying data;
• reasoning;
• consistency with established scientific knowledge;
• assumptions; and
• degree of certainty.

In Ramesh Chandra Agrawal v. Regency Hospital Ltd., the Supreme Court recognised the importance of expert evidence in specialised medical questions and emphasised that expert opinion remains advisory; the court must evaluate the quality and basis of the opinion rather than mechanically accept it.

20. Duty of Candour

An expert should be candid about:

• professional qualifications;
• experience;
• previous opinions;
• limitations;
• uncertainty;
• conflicting scientific literature; and
• facts that weaken the conclusion.

The expert should not conceal material information simply because it may adversely affect the party who has engaged the expert.

This is one of the strongest practical expressions of the expert's duty to the court.

21. Expert Evidence Is Advisory, Not Conclusive

The court is not bound by expert opinion.

This is fundamental.

The judge remains the final decision-maker.

The Supreme Court has repeatedly stated that expert evidence is essentially advisory. In State of H.P. v. Jai Lal, the Court explained that scientific opinion becomes an important factor when it is intelligible, convincing and properly tested, but the judge must independently evaluate it.

Therefore:

Expert opinion assists the court; it does not replace judicial reasoning.

22. Six Important Case Laws

1. State of H.P. v. Jai Lal & Others

(1999) 7 SCC 280

Principle

This is perhaps the leading Indian authority on the duties of an expert.

The Supreme Court held that:

• an expert must possess special knowledge;
• expert evidence is advisory;
• the expert must furnish scientific criteria for assessing the conclusion;
• the opinion must be supported by reasons;
• underlying data and material are important;
• the court must independently evaluate the opinion; and
• an expert report does not automatically become evidence merely because it has been submitted.

Importance

Jai Lal provides the foundational statement of the expert's duty to the court.

2. State (Delhi Administration) v. Pali Ram

(1979) 2 SCC 158

Principle

The case concerned handwriting comparison.

The Supreme Court held that the expert's function is to put before the court the relevant materials and reasons underlying the opinion.

The expert is not the judge of the ultimate issue.

The court must itself evaluate the handwriting evidence with the assistance of the expert.

Importance

The case establishes the important distinction between:

expert assistance and judicial determination.

3. Ramesh Chandra Agrawal v. Regency Hospital Ltd.

(2009) 9 SCC 709

Principle

The Supreme Court considered expert evidence in the context of medical negligence.

It emphasised:

• necessity of expert evidence where the subject lies outside ordinary knowledge;
• appropriate qualifications;
• recognised fields of expertise;
• reliable principles;
• underlying data;
• reasons supporting conclusions; and
• the advisory nature of expert evidence.

Importance

The case demonstrates that an expert opinion must be reasoned, qualified and scientifically grounded, rather than merely asserted.

4. Malay Kumar Ganguly v. Dr. Sukumar Mukherjee

(2010) 2 SCC (Cri) 299 / related 2009 judgment

The Supreme Court considered conflicting medical expert evidence and emphasised that expert evidence must be assessed like other evidence.

The Court reiterated that an expert provides assistance to the court and does not replace the court's own judgment.

Importance

It is particularly relevant to:

• medical negligence;
• conflicting medical opinions;
• evaluation of qualifications;
• scientific reasoning; and
• judicial assessment of expert evidence.

5. Dayal Singh v. State of Uttaranchal

(2012) 8 SCC 263

Principle

The Supreme Court strongly emphasised that an expert must put before the court the material and data that influenced the conclusion.

If the expert does not disclose the relevant similarities, dissimilarities, facts or reasoning, the expert fails to adequately assist the court.

The court should not accept the ipse dixit of an expert.

Importance

This case is particularly useful for the proposition:

An expert must explain, not merely announce, the conclusion.

6. Hazi Mohammed Ikramul Haque v. State of West Bengal

AIR 1959 SC 488

Principle

The Supreme Court approved the rejection of an expert opinion where it amounted merely to an unsupported opinion without adequate reasons.

The principle has subsequently been relied upon in cases such as State of H.P. v. Jai Lal.

Importance

The case establishes an early and enduring principle that unsupported expert opinion has little evidentiary value.

23. Additional Important Authority: Murari Lal v. State of Madhya Pradesh

Murari Lal v. State of Madhya Pradesh, (1980) 1 SCC 704 is also important in relation to handwriting evidence.

The Supreme Court recognised that expert evidence is an aid to judicial determination, rather than a substitute for it. Where expert evidence exists, it assists the court; ultimately the court must perform its own evaluation. The principle has been subsequently reaffirmed by the Supreme Court.

24. Relationship Between Section 39 and Section 45 BSA

The BSA should be read as a connected scheme.

Section 39 — Opinions of experts

Establishes when expert opinion becomes relevant.

Section 40 — Facts bearing upon opinions of experts

Makes relevant facts that support or are inconsistent with expert opinions.

Section 41 — Opinion as to handwriting and signature

Deals specifically with handwriting and signature-related opinion.

Section 45 — Grounds of opinion

Makes the grounds upon which an opinion is based relevant.

The statutory structure therefore reinforces the same principle developed by the Supreme Court:

The conclusion of an expert cannot be separated from the factual and reasoning foundation upon which it rests.

25. Duties of an Expert — Consolidated List

An expert appearing before a court should generally:

26. What an Expert Must Not Do

An expert should not:

1. act as an advocate for the instructing party;
2. suppress unfavourable scientific material;
3. deliberately exaggerate certainty;
4. rely upon irrelevant material;
5. provide an opinion outside his expertise;
6. give conclusions without reasons;
7. ignore contradictory evidence;
8. misrepresent scientific literature;
9. substitute personal belief for scientific analysis;
10. decide questions of law;
11. decide the credibility of witnesses;
12. declare an accused legally guilty or innocent;
13. refuse reasonable scrutiny of methodology; or
14. treat his opinion as binding upon the court.

27. Expert Witness Versus Ordinary Witness

28. Expert Witness Versus Advocate

This distinction is extremely important.

Advocate

An advocate represents the interests of a client.

Expert

An expert assists the court through specialised knowledge.

Therefore, although an expert may be engaged by a party, the expert's professional function is fundamentally different from that of the party's advocate.

An advocate may legitimately argue:

"The evidence supports our client's case."

An expert should instead say:

"Having examined the available material using the relevant methodology, my professional conclusion is X, subject to these limitations."

29. Judicial Evaluation of Expert Evidence

The court should ordinarily consider:

A. Qualifications

Does the witness possess relevant specialised knowledge?

B. Experience

Does the expert have sufficient practical experience?

C. Methodology

Is the methodology appropriate?

D. Data

What facts and material were considered?

E. Reasoning

Does the conclusion logically follow from the material?

F. Consistency

Is the opinion consistent with established scientific knowledge?

G. Contradictions

How does the expert deal with contrary evidence?

H. Cross-examination

Did the expert's opinion withstand meaningful scrutiny?

I. Limitations

Has the expert honestly identified limitations?

J. Overall evidence

Does the expert opinion fit with the remaining evidence?

This approach reflects the Supreme Court's insistence that the court must independently assess expert evidence rather than mechanically accept it.

30. Importance of the Duty in Criminal Trials

Expert evidence can be especially significant in criminal cases involving:

• DNA;
• fingerprints;
• ballistics;
• handwriting;
• toxicology;
• forensic pathology;
• cybercrime;
• digital evidence;
• voice identification;
• narcotics analysis; and
• medical evidence.

Because scientific evidence may appear highly authoritative, there is a danger that the court may give it excessive weight.

The duty of the expert to explain the basis, limitations and degree of certainty helps prevent this problem.

The court remains the ultimate evaluator.

31. Importance in Civil and Commercial Litigation

The same principles apply in:

• medical negligence;
• patent and trademark disputes;
• valuation disputes;
• construction disputes;
• accounting disputes;
• taxation;
• banking;
• environmental litigation;
• corporate disputes;
• intellectual property;
• technology disputes; and
• damages assessment.

For example, a valuation expert should explain the valuation methodology, assumptions, comparable transactions and adjustments rather than simply state a valuation figure.

32. Key Legal Principle

The Supreme Court's jurisprudence can be reduced to the following formula:

Expertise gives the witness the ability to assist; reasoning gives the opinion evidentiary value; independence gives it credibility; and judicial scrutiny gives it legal effect.

An expert therefore has a duty to the court that is higher than the duty to the party who has engaged the expert.

The court must be given sufficient material to independently evaluate the opinion.

33. Conclusion

Under the present Bharatiya Sakshya Adhiniyam, 2023, expert evidence is expressly recognised under Section 39, with related provisions dealing with facts bearing upon expert opinions and the grounds of such opinions.

The Indian Supreme Court's consistent position is that an expert is not a partisan witness, not a substitute judge and not an advocate. The expert's fundamental responsibility is to assist the court by providing competent, objective, intelligible and reasoned specialised knowledge.

The six principal authorities are:

1. State of H.P. v. Jai Lal, (1999) 7 SCC 280 — expert evidence is advisory and must provide scientific criteria and reasons.
2. State (Delhi Administration) v. Pali Ram, (1979) 2 SCC 158 — expert assists the court but cannot assume the judicial function.
3. Ramesh Chandra Agrawal v. Regency Hospital Ltd., (2009) 9 SCC 709 — qualifications, reliable principles and supporting data are essential.
4. Malay Kumar Ganguly v. Dr. Sukumar Mukherjee — expert evidence must be independently evaluated, particularly where medical opinions conflict.
5. Dayal Singh v. State of Uttaranchal, (2012) 8 SCC 263 — an expert must disclose the material and reasons underlying the conclusion; the court cannot rely on mere ipse dixit.
6. Hazi Mohammed Ikramul Haque v. State of West Bengal, AIR 1959 SC 488 — an unsupported expert opinion carries little evidentiary value.

In essence, the expert's duty is to tell the court the truth as supported by specialised knowledge, explain the reasoning transparently, disclose relevant limitations, withstand scrutiny, and leave the ultimate decision to the court.