Law of Equity

"[I]t has been established that, in order that a trust may be created, the subject matter must be certain, the objects of the trust must becertainand the words relied on as creating the trust must have been used in an imperative sense so as to show that the testator intends to create an obligation."

With reference to appropriate case law, critically evaluate what is meant by the 'three certainties' necessary for the creation of an express trust.