High Quality Content by WIKIPEDIA articles! Knight v Knight (1840) 49 ER 58 is an English trusts law case, embodying a simple statement of the "three certainties" principle. This has the effect of determining whether assets can be disposed of in wills, or whether the wording of the will is too vague to allow beneficiaries to collect what appears on the face of the will to be theirs. The case has been followed in most common law jurisdictions.