If contractual obligation depended on consent, it would seem to follow that a material mistake on any matter that induced the consent would prevent the formation of a contract. It was by application of this principle that Pothier asserted that ‘error is the greatest defect that can occur in a contract, for agreements can only be formed by the consent of the parties, and there can be no consent when the parties are in an error respecting the object of their agreement’. He did not hesitate to spell out the far-reaching consequences of this line of thinking: ‘error annuls the agreement, not only when it affects the identity of the subject, but also when it affects that quality of the subject which the parties have principally in contemplation, and which makes the substance of it’, adding, as an illustration, ‘therefore if, with the intention of buying from you a pair of silver candlesticks, I buy a pair which are only plated, though you have no intention of deceiving me, being in equal error yourself, the agreement will be void, because my error destroys my consent; for my intention was to buy a pair of silver candlesticks’. Even where there was reasonable reliance by one party on the apparent consent of the other, as in the case of an artist commissioned to paint a picture by a person privately mistaken as to the artist's identity, Pothier thought that the mistaken party could not be liable on contractual principles, though he might be liable on a non-contractual principle: ‘in this case I am obliged not by the agreement, which was void, and therefore could not produce any obligation; the reason of my obligation is the principle of equity which obliges me to indemnify the person whom I have imprudently led into an error’.