, Common Mistake (Error in Substantia) and the Validity of a Contract for the Sale of a Diamond
Ring
The facts indicate that both Jabu and Raymond concluded the contract on the shared assumption
that the ring in question was a genuine diamond ring. After the sale, it was discovered that the ring
was in fact a fake, made from artificial and inferior materials. The relevant mistake in this scenario
is a common mistake (error communis) relating to the subject matter of the contract, more
specifically a mistake as to the substance or essential quality of the thing sold (error in substantia).
A common mistake occurs where both parties labour under the same misapprehension regarding a
fundamental fact at the time of contracting. In South African law, where the mistake relates to a
material aspect that goes to the root of the agreement, and where there is no true consensus
between the parties, the contract may be void. In this case, both Jabu and Raymond believed that
the object of the sale was a genuine diamond ring. The authenticity of the diamond was not merely
incidental; it constituted the essential characteristic of the merx. The price of R80 000 clearly
reflects that the parties contracted on the basis that the ring was genuine. The fact that the ring is
artificial means that the parties were not ad idem as to the true nature of the subject matter.
The leading authority on material mistake affecting consensus is Sonap Petroleum (SA) (Pty) Ltd v
Pappadogianis 1992 (3) SA 234 (A), where the court held that a contract will be void if there was no
true consensus between the parties, and the mistake is material and reasonable (at 239I–240B).
Although that case dealt with unilateral mistake, it reaffirmed the broader principle that true
agreement (consensus ad idem) is a requirement for a valid contract. In the present matter, the
mistake is even stronger because it is common to both parties.
Furthermore, in Dickinson Motors (Pty) Ltd v Oberholzer 1952 (1) SA 443 (A), the Appellate Division
recognised that a mistake relating to the identity or essential characteristics of the merx can
exclude consensus and render the contract void (at 450–451). Similarly, where the parties contract
for one thing but in reality another thing is delivered, there is no true agreement. A diamond ring
and an artificial imitation are fundamentally different in substance and commercial value. This
constitutes error in substantia, which traditionally renders a contract void if the mistake relates to a
quality regarded by both parties as essential.
The mistake in this scenario is not merely a mistake as to value (error in qualitate), which generally
does not invalidate a contract. The distinction is important. A mistake about market value would
not render the contract void, but a mistake about the essential nature or identity of the object does.
Here, the genuineness of the diamond is the very basis of the transaction. Without that quality, the
ring is something entirely different from what both parties believed they were contracting for.
Therefore, because the mistake relates to the essential nature of the subject matter and was
common to both parties, there was no true meeting of the minds. The contract is void ab initio due
to common mistake as to substance. Raymond is entitled to treat the contract as void and may
recover the purchase price paid. Since the contract is void and not merely voidable, it is regarded as
if it never legally existed.
Ring
The facts indicate that both Jabu and Raymond concluded the contract on the shared assumption
that the ring in question was a genuine diamond ring. After the sale, it was discovered that the ring
was in fact a fake, made from artificial and inferior materials. The relevant mistake in this scenario
is a common mistake (error communis) relating to the subject matter of the contract, more
specifically a mistake as to the substance or essential quality of the thing sold (error in substantia).
A common mistake occurs where both parties labour under the same misapprehension regarding a
fundamental fact at the time of contracting. In South African law, where the mistake relates to a
material aspect that goes to the root of the agreement, and where there is no true consensus
between the parties, the contract may be void. In this case, both Jabu and Raymond believed that
the object of the sale was a genuine diamond ring. The authenticity of the diamond was not merely
incidental; it constituted the essential characteristic of the merx. The price of R80 000 clearly
reflects that the parties contracted on the basis that the ring was genuine. The fact that the ring is
artificial means that the parties were not ad idem as to the true nature of the subject matter.
The leading authority on material mistake affecting consensus is Sonap Petroleum (SA) (Pty) Ltd v
Pappadogianis 1992 (3) SA 234 (A), where the court held that a contract will be void if there was no
true consensus between the parties, and the mistake is material and reasonable (at 239I–240B).
Although that case dealt with unilateral mistake, it reaffirmed the broader principle that true
agreement (consensus ad idem) is a requirement for a valid contract. In the present matter, the
mistake is even stronger because it is common to both parties.
Furthermore, in Dickinson Motors (Pty) Ltd v Oberholzer 1952 (1) SA 443 (A), the Appellate Division
recognised that a mistake relating to the identity or essential characteristics of the merx can
exclude consensus and render the contract void (at 450–451). Similarly, where the parties contract
for one thing but in reality another thing is delivered, there is no true agreement. A diamond ring
and an artificial imitation are fundamentally different in substance and commercial value. This
constitutes error in substantia, which traditionally renders a contract void if the mistake relates to a
quality regarded by both parties as essential.
The mistake in this scenario is not merely a mistake as to value (error in qualitate), which generally
does not invalidate a contract. The distinction is important. A mistake about market value would
not render the contract void, but a mistake about the essential nature or identity of the object does.
Here, the genuineness of the diamond is the very basis of the transaction. Without that quality, the
ring is something entirely different from what both parties believed they were contracting for.
Therefore, because the mistake relates to the essential nature of the subject matter and was
common to both parties, there was no true meeting of the minds. The contract is void ab initio due
to common mistake as to substance. Raymond is entitled to treat the contract as void and may
recover the purchase price paid. Since the contract is void and not merely voidable, it is regarded as
if it never legally existed.
