What is a provisional sum in a builder's quote?

When part of the work cannot be priced at quote stage - the kitchen not yet chosen, the ground not yet opened, the drainage run not yet designed - the builder puts in a provisional sum: a stated allowance that stands in the total until the real cost is known. It is honest practice in itself; the trouble is what it does to comparisons and expectations. A quote's bottom line is only as firm as its softest lines, and a total leaning on generous provisional sums is really a smaller firm price plus a set of guesses - each one adjusted later, usually upwards, without competition. Before signing: know exactly which lines are provisional, ask what each allowance would actually buy at today's prices, and have the adjustment mechanism - how the real cost replaces the allowance - written into the contract. Then watch each one as it lands during the build.