The three certainties are a set of requirements that must be met in order to create a valid trust. These are:
Certainty of intention: The settlor must have intended to create a trust. This means that there must be clear evidence that the settlor intended to transfer legal ownership of the property to the trustee, and intended for the beneficiaries to have a beneficial interest in the trust property.
Certainty of subject matter: The property that is being transferred into the trust must be clearly identified and defined. The trust property must be capable of being distinguished from other property, and the interests of the beneficiaries in that property must be capable of being ascertained.
Certainty of objects: The beneficiaries of the trust must be clearly identified or ascertainable. This means that the beneficiaries must be identifiable by name or by class, such as "my children" or "my employees". The trust must not be so uncertain that it is impossible to determine who the beneficiaries are, or to determine the extent of their interests in the trust property.
If any of these three certainties is missing, then the trust will not be valid. The purpose of these requirements is to ensure that the trust is legally enforceable, and that the trustee knows what their duties and obligations are, and who they owe those obligations to.