Have you ever signed a document without fully understanding what it was? Perhaps you were told it was one thing, but it turned out to be something completely different? In Nigerian contract law, there’s a legal defense called “non est factum” that can protect you in such situations—but only under very specific circumstances.

This guide explains what non est factum means, when you can use it, and how Nigerian courts decide whether someone can escape a contract they signed by mistake.

What Does Non Est Factum Mean?

Non est factum is a Latin phrase that literally means “it is not my deed.” It’s a defense in contract law that allows someone to claim they’re not bound by a document they signed because they were fundamentally mistaken about what they were signing.¹

The basic principle is simple: if you sign a document believing it to be one type of document, but it’s actually something completely different, you may be able to argue that the contract is void (invalid from the beginning).

However, this defense is very difficult to succeed with. Nigerian courts don’t allow people to escape contracts simply because they didn’t read what they signed or were careless. The law generally holds that when you sign a document, you’re bound by its terms whether you read it or not.²

Why Does Non Est Factum Exist?

The doctrine of non est factum was originally developed in England centuries ago to protect people who couldn’t read. In Thoroughgood’s Case (1584), an illiterate man was tricked into signing a deed that he thought waived rent owed to him, but actually transferred his property. The court held he wasn’t bound by the deed because he couldn’t read it and was deceived.³

In Nigeria, this doctrine is particularly important because of widespread illiteracy. According to various studies, Nigeria’s illiteracy rate exceeds 50% in many regions.⁴ Many Nigerians cannot read English or may not understand complex legal documents, making them vulnerable to fraud and deception in contractual dealings.

To address this, Nigeria has the Illiterates Protection Act 1958, which provides additional safeguards for illiterate persons entering into contracts. This Act requires that when an illiterate person signs a document, it must be read over and explained to them in a language they understand, and a certificate to this effect must be endorsed on the document.⁵

The Two Essential Requirements for Non Est Factum

For non est factum to succeed in Nigerian law, you must prove two things:

1. Fundamental Difference in Nature

There must be a radical or fundamental difference between what you thought you were signing and what you actually signed. The document must be of an entirely different character or class, not just different in its details or terms.

The landmark case establishing this requirement is Foster v Mackinnon.⁶ In that case, an elderly man with poor eyesight was induced to sign what he thought was a guarantee (a promise to pay someone else’s debt if they defaulted). In reality, it was a bill of exchange for £3,000 with him as the primary debtor—a completely different type of obligation. The court held that because the documents were fundamentally different in nature, he could plead non est factum.

What counts as fundamentally different?

Nigerian courts have held that the following differences are fundamental enough:

• Signing a mortgage thinking it’s a receipt⁷
• Signing a sale agreement thinking it’s a lease
• Signing a power of attorney thinking it’s a will
• Signing a transfer of property thinking it’s an acknowledgment of payment

What doesn’t count as fundamentally different?

The following mistakes are NOT enough for non est factum:

• Signing a sale agreement at ₦5 million when you thought it was ₦3 million (same type of document, just different terms)
• Signing a lease for 10 years when you thought it was for 5 years
• Signing a loan agreement with 15% interest when you thought it was 10%
• Misunderstanding specific clauses or conditions in a contract

The key question is: are you mistaken about the nature or character of the document, or just about its content or terms? Only mistakes about the nature of the document qualify for non est factum.

This distinction was emphasized in the Nigerian case of Egbase v Oriareghan,⁸ where the Supreme Court held that the plea of non est factum requires proof that the document signed was of a fundamentally different character from what the signer intended.

2. No Negligence on Your Part

Even if the document is fundamentally different, you cannot succeed with non est factum if you were careless or negligent. You must show that you took reasonable care in the circumstances.

The principle was clearly stated in Foster v Mackinnon: a person seeking to rely on non est factum must not have been guilty of negligence.⁹

What counts as negligence?

You will be considered negligent if you:

• Could read but simply didn’t bother to read the document before signing
• Had the opportunity to ask questions but didn’t
• Signed blank papers and allowed someone else to fill in the details later
• Ignored obvious warning signs or suspicious circumstances
• Failed to seek help when you didn’t understand something and could have done so

What doesn’t count as negligence?

You are NOT negligent if:

• You’re illiterate and the document wasn’t properly explained to you
• You’re blind or have a disability that prevented you from reading
• You asked to see the full document but were deliberately misled
• You took reasonable steps to understand but were deceived by fraud

In Saunders v Anglia Building Society,¹⁰ an elderly woman signed a document transferring her house to someone, thinking it allowed her nephew to borrow money against it. She claimed her glasses were broken at the time. The House of Lords held that breaking your glasses doesn’t excuse you from taking other precautions, like asking someone to read the document to you or waiting until you could see properly. Her claim failed because she was negligent.

Non Est Factum in Nigeria: The Illiterates Protection Act

Nigeria’s legal system recognizes that a large portion of the population cannot read or write. The Illiterates Protection Act 1958 provides special protections for illiterate persons.

Under this Act, when an illiterate person executes a deed or document by making their thumbprint or mark, the following requirements must be met:

1. The document must be read over and explained to the illiterate person in a language they understand
2. The person must appear to understand the document
3. A certificate must be endorsed on the document stating that these steps were followed
4. The certificate must be signed by a magistrate, justice of the peace, or other authorized person

If these requirements aren’t followed, the illiterate person can challenge the document’s validity.¹¹

This was demonstrated in the Nigerian case of Adegbokun v Akinsanya,¹² where an illiterate man signed a document conveying the wrong property. The buyer knew the man’s true intention, but the contract was not properly explained to him. The court held the contract was void, emphasizing the need to protect vulnerable parties from mistakes they couldn’t reasonably avoid due to illiteracy.

Important Nigerian Cases on Non Est Factum

Adegbokun v Akinsanya

This case perfectly illustrates how Nigerian courts apply non est factum to protect illiterate persons. The plaintiff was illiterate and intended to convey one piece of property but ended up signing a document that conveyed a different property. The defendant knew of the plaintiff’s true intention but took advantage of his illiteracy.

The court held the contract void, stating that the document was not properly explained to the illiterate man, and he had no understanding of what he was actually signing. This case shows the court’s willingness to protect disadvantaged parties who cannot read.¹³

Sylvester Egbase v Augustine Oriareghan

The Supreme Court of Nigeria examined non est factum in this case and affirmed that significant contractual differences must be proven. The court emphasized that the plea is not a tool for fraud but rather protection to ensure that a person is not bound by terms of a document they shouldn’t have signed due to fraud or mistake.¹⁴

Justice Karibi-Whyte stated: “It must be noted that the plea of non est factum is not one through which fraud can be perpetuated. The protection offered by the law is to ensure that a person is not held bound by the terms of a document which he should not have signed, but signed due to fraud or mistake.”

When Can You Use Non Est Factum? A Practical Guide

Based on Nigerian law and case precedents, here’s when you might successfully plead non est factum:

You CAN use non est factum if:

• You’re illiterate and the document wasn’t read over or explained to you properly
• You’re blind or have a serious disability that prevented you from knowing what you signed
• Someone deliberately tricked you by showing you only part of the document
• You asked what the document was and were deliberately given false information
• The document you signed is completely different in character from what you were told (e.g., told it was a receipt but it was actually a sale agreement)
• You took reasonable steps to protect yourself but were still deceived

You CANNOT use non est factum if:

• You simply didn’t bother to read the document before signing
• You understood you were signing a contract but didn’t read the specific terms
• You were careless or lazy in protecting your own interests
• The difference is only in the terms or amount, not the type of document
• You signed blank papers and let someone fill them in later
• You had the ability to read or get help but chose not to

The Legal Effect of Non Est Factum

When non est factum succeeds, the contract is void ab initio, which means it’s invalid from the very beginning. Legally, it’s as if the contract never existed at all.

The consequences include:

1. Neither party can enforce the contract
2. Any money paid must be returned
3. Any property transferred must be given back
4. The contract cannot be ratified or confirmed later
5. Third parties who acquired rights under the void contract may also be affected

However, if you signed the document negligently, the contract remains valid and enforceable, even if you were mistaken about its nature.

Non Est Factum vs Other Mistake Doctrines

It’s important to distinguish non est factum from other types of mistakes in contract law:

For more on common and mutual mistake, see our guide on mutual mistake and common mistake in Nigerian contract law.

Non est factum is specifically about signing documents. The other mistake doctrines apply to oral contracts and other situations where no signature is involved.

The Burden of Proof

If you claim non est factum, you have the burden of proving it. This means you must provide clear and convincing evidence that:

1. The document you signed was fundamentally different from what you thought
2. You were not negligent or careless

The standard of proof is high because the courts want to maintain the security and certainty of commercial transactions. If people could easily escape signed contracts by claiming they didn’t understand them, business dealings would become unreliable.¹⁵

Modern Relevance of Non Est Factum in Nigeria

Some legal scholars have questioned whether non est factum is still relevant in modern Nigeria, arguing that:

• Literacy rates are improving
• More people have access to legal advice
• Electronic contracts and digital signatures raise new issues
• The doctrine can be abused by dishonest people trying to escape valid contracts

However, the majority view is that non est factum remains vital in Nigeria because:

• Illiteracy is still widespread, especially in rural areas
• Many Nigerians still cannot afford legal representation
• Vulnerable people need protection from fraud and exploitation
• The strict requirements (fundamental difference + no negligence) prevent abuse

The Illiterates Protection Act 1958 continues to be applied by Nigerian courts, showing that the legal system recognizes the ongoing need to protect disadvantaged parties.¹⁶

Practical Advice: How to Protect Yourself

Whether you can read or not, here are steps to protect yourself when signing any document in Nigeria:

Before Signing:

1. Never sign anything you don’t understand. If you can’t read, insist that someone you trust reads and explains it to you in your language.
2. Ask questions. If anything is unclear, ask for clarification. Write down the answers if possible.
3. Read the entire document. Don’t just read the first page or the signature page. Fraudsters often hide important terms on inner pages.
4. Take your time. Don’t let anyone pressure you to sign quickly. If they rush you, that’s a red flag.
5. Get independent advice. If the document is important (like transferring property or taking a loan), consult a lawyer or someone knowledgeable before signing.
6. Never sign blank papers. Don’t sign documents with blank spaces that can be filled in later.

If You’re Illiterate:

1. Insist on compliance with the Illiterates Protection Act—the document must be read and explained to you, with a proper certificate.
2. Have a trusted person present when you sign, preferably someone who can read and write.
3. Use a magistrate or justice of the peace to witness your signature when possible.

After Signing:

1. Keep copies of all documents you sign.
2. If you discover you were deceived, act immediately. Don’t wait. The longer you wait, the harder it becomes to challenge the contract.
3. Consult a lawyer as soon as possible if you believe you signed something by mistake.

Relationship to Contract Formation Principles

Non est factum relates to broader principles of contract formation in Nigerian law. For a contract to be valid, there must be:

• Offer and acceptance with genuine consensus ad idem (meeting of minds)
• Intention to create legal relations
• Capacity to contract
• Consideration
• Legality

Non est factum challenges the existence of genuine consent. If your mind didn’t accompany your signature because you were fundamentally mistaken about what you were signing, there’s no true agreement.

For more on contract formation, see our guides on the nature of contract and formation of contract.

Conclusion

Non est factum is a narrow but important defense in Nigerian contract law. It protects people who sign documents under fundamental mistakes about what they’re signing—but only if they weren’t careless.

To successfully plead non est factum in Nigeria, you must prove:

1. The document you signed was radically different in nature from what you thought (not just different in terms or amount)
2. You were not negligent—you took reasonable care in the circumstances

For illiterate Nigerians, the Illiterates Protection Act 1958 provides additional safeguards, requiring that documents be properly read over and explained before signing.

The key lesson: always make sure you genuinely understand what you’re signing. Read documents carefully, ask questions, seek advice when needed, and never let anyone rush or pressure you into signing something you don’t fully comprehend.

Remember, the law will not rescue you from your own carelessness, but it will protect you from being victimized by fraud or deception when you’ve taken reasonable steps to protect yourself.

If you believe you’ve signed a document by mistake, consult a lawyer immediately. Time is critical in these situations.

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References

Footnotes

1. Foster v Mackinnon (1869) LR 4 CP 704. ↩

2. L’Estrange v F Graucob Ltd [1934] 2 KB 394. ↩

3. Thoroughgood’s Case (1584) 2 Co Rep 9a. ↩

4. Samuel Korie, ‘The Principle of Non Est Factum and its Application to Contractual Obligations in Both English and Nigerian Law’ (2018) SSRN Working Paper https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3159277 accessed 11 January 2026. ↩

5. Illiterates Protection Act 1958, ss 1-3. ↩

6. Foster v Mackinnon (1869) LR 4 CP 704. ↩

7. See discussion of various scenarios in ‘A Brief Analysis of the Doctrine of Non Est Factum’ (Nigerian Law Claz, 2017) https://www.nigerianlawclaz.com/2017/08/a-brief-analysis-of-doctrine-of-non-est.html accessed 11 January 2026. ↩

8. Sylvester Egbase v Augustine Oriareghan [1991] 8 NWLR (Pt 210) 318 (SC). ↩

9. Foster v Mackinnon (1869) LR 4 CP 704, 711 (Byles J). ↩

10. Saunders v Anglia Building Society (also known as Gallie v Lee) [1971] AC 1004 (HL). ↩

11. Illiterates Protection Act 1958. ↩

12. Adegbokun v Akinsanya discussed in ‘Mistake’ (Learn Nigerian Law) https://www.learnnigerianlaw.com/learn/contract-law/mistake accessed 11 January 2026. ↩

13. ibid. ↩

14. Sylvester Egbase v Augustine Oriareghan [1991] 8 NWLR (Pt 210) 318 (SC) per Karibi-Whyte JSC. ↩

15. Saunders v Anglia Building Society [1971] AC 1004, 1016 (Lord Reid). ↩

16. Onyekachi Duru, ‘The Plea of Non Est Factum is No Longer Valid in Present Day Nigeria – Do You Agree?’ (2012) SSRN Working Paper https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2147372 accessed 11 January 2026. ↩