For any Will to be valid, the will-maker must know what they are making a Will, be aware of their estate, be aware of the persons they wish to benefit and be able to consider those persons who would normally be expected to receive an inheritance under their Will. This is called having testamentary capacity. A will-maker who suffers from mental disability or delusion may or may not have the necessary capacity to make a valid will. In some cases, a lack of testamentary capacity can be caused by the effect of medication.