Unusually, I agree totally with Ann Minogue (3 December, page 49).

Her demolition job on provisional sums absolutely hits its target. 鈥淒efined鈥� provisional sums are a nonsense. However, her article is too good an opportunity to miss the chance to expose a few other myths about provisional sums. Nothing much has changed since I entered the industry in the 1950s.

All on the design side of the industry need to ask why provisional sums are necessary anyway. Some of the reasons for including them in the contract include: the client cannot make up his mind and is holding up the programme; the design team has run out of time, leaving aspects still to be designed; the architect cannot conceptualise what he wants until he sees the space to put it in (in Ann鈥檚 example, the reception desk).

I make no judgment on the legitimacy of any of these reasons, but the way the provisional sum is conceived is worthy of note. Typically the QS, exasperated at the lack of detail, has to threaten the design team with provisional sums if they will not or cannot be a bit more specific. If that fails, he has to estimate the cost of the work and includes a provisional sum (or sums) sufficient that the final cost will not come as too great a shock to the client. If it is transparently handled, the device can be a proper component of the contract processes. If it is slipped in as an attempt to protect a badly performing designer, a darker side emerges.

The degree of transparency may affect the builder more than the other players. What sense is he supposed to make of a major provisional sum when he is committing himself to completing the job by a given date? This is where I might just permit the JCT鈥檚 muddled logic a gleam of hope. I have known designers who can provide the contractor with a sketch of the work in sufficient detail for it to anticipate what will be required. Hence a possible justification of a 鈥渄efined鈥� sum, and the inference that the work can be valued at contract rates without recourse to extensions and loss and expense. But the job can be done just as well without the need for two versions of the provisional sum. So Ann is still right: it is a nonsense.

Malcolm Taylor, via email

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