# The three certainties for express private trusts

> **Key takeaway:** Three certainties (Knight v Knight): intention, subject matter, objects. Discretionary objects: 'is or is not' test (McPhail v Doulton); conceptual certainty required. Fixed trusts: list certainty traditionally required. Subject matter must be identifiable (Hunter v Moss relevant for identical intangibles).

- **Jurisdiction:** England & Wales
- **Practice area:** Trusts And Chancery
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/TrustsAndChancery/three-certainties
- **Keywords:** three certainties, certainty of objects, McPhail v Doulton, Knight v Knight, express trust, discretionary trust, Hunter v Moss, precatory words

## What is this about?

An express private trust will not be valid unless the three certainties are satisfied: certainty of intention, certainty of subject matter, and certainty of objects. The doctrine polices whether a settlor has really created a trust (as opposed to a gift, moral obligation, or failed attempt) and whether trustees (and the court) can administer it.

## What is the core rule?

For an express private trust: (1) Intention — the settlor must intend to impose a mandatory trust obligation, not merely express a wish (precatory words are not automatically fatal but are scrutinised in context). (2) Subject matter — the trust property and, where relevant, the beneficial shares must be conceptually certain and identifiable. (3) Objects — the beneficiaries must be defined with sufficient certainty: fixed trusts generally require conceptual certainty and, traditionally, the ability to draw up a complete list; discretionary trusts are tested by the 'is or is not' criterion of conceptual certainty (McPhail v Doulton), subject to administrative workability.

## What are the elements or test?

1. Certainty of intention: do the words and conduct, read in context, show an intention to create a trust rather than a gift, agency, or non-binding wish?
2. Certainty of subject matter: is the property clearly identified? If residual/unascertained property is involved, can it be identified (contrast cases on bulk goods / shares — see e.g. Hunter v Moss for identical intangible property vs uncertain bulk problems)?
3. Certainty of objects (fixed trust): can the class be defined conceptually and, where required, can a complete list of beneficiaries be compiled?
4. Certainty of objects (discretionary trust): is it possible to say of any given postulant whether they are or are not within the class (McPhail v Doulton), and is the trust administratively workable?

## Which authorities matter?

- **Knight v Knight (1840) 3 Beav 148** — Classic statement of the three certainties requirement.
- **McPhail v Doulton [1971] AC 424** — House of Lords adopts the 'is or is not' test for certainty of objects in discretionary trusts (aligning with the powers test in Re Gulbenkian).
- **Re Baden's Deed Trusts (No 2) [1973] Ch 9** — Court of Appeal explores conceptual vs evidential certainty under the McPhail test; conceptual uncertainty is fatal, evidential difficulty is not necessarily so.
- **Hunter v Moss [1994] 1 WLR 452** — Illustrates subject-matter certainty for a trust of a portion of identical shares (intangible property) without segregation — still important and sometimes contrasted with tangible bulk cases.

## How does this apply in practice?

Limited to express private trusts. Charitable trusts have different objects rules (public benefit / charitable purpose certainty). Resulting and constructive trusts do not depend on the settlor's three-certainties exercise in the same way. Always read the instrument as a whole; labels ('trust', 'request', 'desire') are not conclusive.

## What are common pitfalls?

- Treating precatory words as automatically creating or defeating a trust without contextual construction
- Applying the complete-list test to a discretionary trust after McPhail v Doulton
- Confusing conceptual uncertainty (fatal) with mere evidential difficulty in identifying members of a conceptually clear class
- Assuming any uncertainty as to quantum of beneficial shares can always be cured by equal division — it depends on the wording and type of uncertainty

## When would a practitioner use this?

Use when drafting or challenging lifetime settlements, wills that may create trusts, or when advising whether an informal family arrangement has created a trust of property or money.

## Quick reference

Three certainties (Knight v Knight): intention, subject matter, objects. Discretionary objects: 'is or is not' test (McPhail v Doulton); conceptual certainty required. Fixed trusts: list certainty traditionally required. Subject matter must be identifiable (Hunter v Moss relevant for identical intangibles).

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*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*