1. Meaning and Legal Concept

A testator is said to have mental capacity if they can:

1. Understand the nature of making a will and its legal effect
2. Understand the extent of their property
3. Comprehend the claims of persons who may expect benefit (family, dependents, etc.)
4. Be free from any mental disorder or delusion that affects the disposition of property

This test is functional, not medical—a person may have a mental illness but still possess capacity during a “lucid interval”.

2. Leading Case: Banks v Goodfellow (1870)

This is the foundational case on testamentary capacity.

Facts:

The testator suffered from delusions but still made a will leaving property to his niece.

Held:

The will was valid because the delusions did not affect the testamentary decisions.

Principle Established:

A testator must:

• Understand the act of making a will
• Understand property being disposed of
• Understand moral/legal claims of beneficiaries
• Not be influenced by insane delusions

This case introduced the “sound disposing mind” test, still applied worldwide.

3. Essential Elements of Mental Capacity

(A) Understanding the Act

The testator must know they are making a will and its effect after death.

(B) Understanding Property

They must broadly understand what assets they own.

(C) Understanding Claims

They must recognise persons who might reasonably expect to benefit.

(D) Absence of Disorder Affecting Judgment

Any mental disorder must not influence decisions in the will.

4. Presumption of Capacity

Law generally presumes that:

Every adult testator has mental capacity unless proven otherwise.

The burden of proof lies on the person challenging the will.

5. Important Case Laws on Mental Capacity of Testator

Below are important supporting case laws (beyond Banks v Goodfellow):

1. Banks v Goodfellow (1870)

• Established the classical four-part test
• Delusions only invalidate a will if they influence dispositions

2. Waring v Waring (1848)

• Earlier stricter approach
• Suggested broader incapacity due to mental disorder
• Later rejected in favour of Banks v Goodfellow

3. Harwood v Baker (1840)

• Recognised that undue influence + weakened mind may affect capacity
• Showed courts scrutinise suspicious wills more strictly when testator is weak or ill

4. Boughton v Knight (1873)

• Confirmed that capacity requires “sound and disposing mind”
• Court held mere old age or illness is not enough to invalidate a will

5. Re Walker (1871)

• Held that testator must understand extent of property and claims of beneficiaries
• Reinforced that partial understanding is not sufficient if essential comprehension is missing

6. Re Estate of Park (1954)

• Court emphasised medical evidence alone is not decisive
• Focus is on actual understanding at the time of execution

7. Key v Key (2010) (modern authority)

• Elderly testator made unusual will after spouse’s death
• Court found lack of capacity due to grief-induced mental disorder
• Reaffirmed application of Banks v Goodfellow in modern disputes

8. Re Morris (1970)

• Confirmed that lucid intervals are valid for will-making
• Even mentally ill persons can make valid wills if lucid at execution

6. Role of Medical Evidence

Courts consider:

• Psychiatric reports
• Hospital records
• Behaviour before and after execution
  But legal capacity is determined by judicial assessment, not medical diagnosis alone.

7. Practical Importance

Mental capacity is crucial in:

• Probate disputes
• Elderly testator wills
• Cases involving dementia, depression, or psychiatric illness
• Allegations of undue influence

8. Conclusion

Mental capacity of a testator ensures that a will reflects the true and free intention of the person making it. The law balances:

• Freedom of testamentary disposition
• Protection of vulnerable individuals

The guiding principle remains Banks v Goodfellow, supported and refined by later decisions such as Boughton v Knight, Harwood v Baker, and Key v Key.