Must, shall, and will are all used in modern contracts to express obligations: Friends Life Ltd v Siemens Hearing Instruments Ltd [2014] EWCA Civ 382, paragraph 59; Hoffman v Finalto Group Ltd [2026] EWHC 921 (Comm) (21 April 2026), paragraphs 63-64, 66.

But do they all work equally well and, if not, what can contract drafters do about it?

What is the difference in meaning?

As we know, every word of a contract is interpreted in context and according to business sense. Black can mean white, if that’s what the parties must have meant. Therefore:

  • Any word can create an obligation. A contract can impose obligations by any words. For example, this wording in a collective agreement created an obligation, although it appeared permissive: '… the contract of a musician may be terminated after the following procedure has been followed …': Johnston v Welsh National Opera Ltd [2011] EAT 20.5.11, upheld in [2012] EWCA Civ 1046.
  • No word is guaranteed to create an obligation. There is no magic word that always creates a duty, regardless of context and business sense. For example, this wording in a referral agreement did not create an obligation: '… Motorplus Ltd shall refer a quantity of [specified type] claims to PM Law Ltd Solicitors …': PM Law Ltd v Motorplus Ltd [2018] EWCA Civ 1730.

As drafters, we want to express the parties’ intention, not to create a misleading impression that context and business sense might correct. Given that any word can create an obligation but none inevitably will, which is most likely to do so? Dictionaries suggest:

  1. Must: generally conveys necessity, not the future.
  2. Shall: I/we shall indicates the future in a formal and old-fashioned tone. You/he/she/it shall once conveyed necessity but is now largely obsolete.
  3. Will: generally expresses the future.

(The traditional distinction between shall and will was never consistently followed and is now largely outdated.)

Tone and use matter more than meaning

In tone, must is the most commanding, making it unwelcome in contracts meant to reflect willing agreement between equals.

Shall also sounds commanding: so much so that one judgment accidentally interpreted it as mandatory in a duration clause, before correcting this first impression to reflect context and business sense in an addendum: Gama Aviation (UK) Ltd v Mwwmmwm Ltd [2022] EWHC 1191 (Comm).

But shall is not reliably mandatory in contracts because of its widespread use and misuse for many other purposes. Such inconsistent drafting can fuel an argument along these lines:

Party: Excuse me, Otherparty, you are in breach of clause X.

Otherparty: No, clause X says shall but look at clauses Y and Z, where shall can’t have imposed an obligation. So I say clause X is only directory, not mandatory. That makes commercial sense, considering the context, because …

This wording from a lease illustrates the point in one long, archaic sentence:

'If the Landlords shall fail to exercise their right to require the rent payable hereunder to be reviewed within the relevant period prescribed in paragraph 1(1) hereof or in the event that by the relevant date of review the Landlords and the Tenants shall not have reached agreement and the valuer (if appointed) shall not have given his decision provided for in paragraph 2 hereof then the Tenants shall continue to pay rent at the rate of the rent payable before the relevant date of review on each day appointed by this Deed for payment of rent until agreement shall be reached or the said decision shall be made whichever shall first occur.' (emphasis added)

Of the seven shalls, only one imposes an obligation (to keep paying rent at the old rate). Replacing shall with must or will produces the same result – only one obligation – and will makes the six other uses sound as unnatural as shall does to a non-lawyer: 'If the Landlords will fail …'.

Lawyers don’t make this mistake with must, perhaps because must is still familiar everyday language, easy to use correctly.

Practical drafting

The well-known advice works well here: use one word consistently to express obligations and for nothing else. To achieve this, must is the safest choice. And draft in the present tense.

Then, whenever must appears, make sure you identify who must do what and when, and that they are a contracting party, correcting some other common problems when drafting obligations.

Finally, if you find must too commanding, even for a contract, change it to your preferred word: if not shall or will, then another alternative, such as has to, which is both modern and mandatory.

At this point, I suggest you avoid shall. Lawyers may feel comfortable with its traditional tone, but does shall work equally well for the contract’s users? Do they appreciate the familiar language, finding it speeds up review, smooths negotiation and promotes understanding and compliance? Or is shall subtly working against you? As you labour to deliver timely, commercial and watertight contracts, does your work product whisper something along these lines, undermining your client relations and marketing messages? 'We are lawyers, you are not. We don’t speak your language. If we understand your needs, we don’t care about them. Live with it.'

If that’s the subtext to your contracts, think again about must and will.

 

Daphne Perry is an ex-lawyer, consultant, writer and trainer on plain English for law and business

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