Principle: Mere silence as to facts likely to affect the willingness of a person to enter into a contract is not fraud, unless the circumstances of the case are such that, regard being had to them, it is the duty of the person keeping silence to speak, or unless his silence is, in itself, equivalent to speech. Facts: A sells, by auction, to B, a horse which A knows to be unsound. A says nothing to B about the horse’s unsoundness.