Why vague qualitative terms invite disputes
Commercial contracts are full of undefined qualitative words: reasonable, material, substantial, promptly, commercially reasonable. Each pushes a hard question into the future, to be answered with hindsight if the relationship sours. The most fought-over of these are the endeavours obligations.
They feel like agreement at the time of drafting, but they often just postpone the disagreement to the moment it costs the most.
The endeavours hierarchy
The three common formulations sit on a ladder. Reasonable endeavours is the lightest: the party must take one reasonable course towards the objective, can usually prefer its own commercial interests, and need not act against them. All reasonable endeavours is more demanding, requiring the party to exhaust the reasonable options and possibly to subordinate some of its own interests; courts vary on how close it sits to best endeavours.
Best endeavours is the heaviest: the steps a prudent, determined and reasonable person would take, in their own interest and wanting to achieve the result. It can require acting against the party's own commercial interests, though not usually to the point of financial ruin.
RTI v MUR Shipping: the limit on endeavours
In RTI Ltd v MUR Shipping BV [2024] UKSC 18, the Supreme Court considered a reasonable endeavours proviso in a force majeure clause after US sanctions disrupted dollar payments and the charterer offered to pay in euros instead. The Court held that, absent clear words, a reasonable endeavours obligation is geared towards achieving contractual performance, not accepting a substitute for it.
So the affected party did not have to accept non-contractual performance to overcome the force majeure event. The case is a reminder that endeavours wording is read against what the contract actually requires, and does not silently rewrite the bargain.
Endeavours are fact-sensitive
What any endeavours obligation requires depends heavily on the circumstances, judged at the time of performance rather than at signing. That uncertainty is the whole problem: two reasonable people can disagree about what reasonable required, and only a court will settle it.
That is acceptable for genuinely uncertain future actions. It is a poor choice where you actually know what you need the other side to do.
Replace vague terms with concrete obligations
Where an outcome matters, specify it. Instead of reasonable endeavours to deliver on time, set out the steps: allocate named resources, notify within a fixed period of any anticipated delay, arrange a backup source if the primary fails, and bear the cost of expedited shipping if needed. Instead of material, set a threshold ("exceeding GBP 50,000 or 10% of annual contract value"). Instead of promptly, give a number ("within 5 business days").
Concrete obligations are easier to perform, easier to enforce, and far less likely to end in an argument about what a word meant.
Use at the desk
Practical checklist
- Know the hierarchy: reasonable, then all reasonable, then best endeavours, in increasing burden.
- Remember reasonable endeavours aim at contractual performance, not a substitute, absent clear words (RTI v MUR Shipping [2024] UKSC 18).
- Where an outcome matters, replace endeavours with concrete steps, resources, and deadlines.
- Define material with a threshold (for example, a figure or a percentage of contract value).
- Replace promptly and without delay with a measurable timeframe (for example, within 5 business days).
- In review, flag undefined qualitative terms in obligations you care about enforcing.
This guide is informational only and is not legal advice. It does not replace advice from licensed counsel on the facts of a specific transaction.
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