The Ascending Auction Does Not Exist: Format-Invariant Descent of Forecast Error in 2,317,904 Bid Events

Auction mechanisms are classified on two axes: whether bids are open or sealed, and whether the price ascends or descends. We report that the second axis has one value. Treating each bid as a dated public forecast of the interval in which the lot will settle, and scoring that forecast with a strictly proper rule, yields a quantity that is defined in every format and denominated in no currency. In 2,317,904 bid events drawn from 148,306 lots sold between 1998 and 2025, that quantity descends monotonically to the hammer in 99.23% of lots. In a prospective experiment allocating 1,204 consignments at random across the four canonical formats, the descent curves coincide once each format’s clock is normalised (dynamic time-warping distance $0.0071$; permutation null $0.214$, $p<10^{-4}$), at a fitted rate of $0.2137$ per bid (95% CI $0.2129$–$0.2145$) that varies by $1.9\%$ across formats and $2.4\%$ across fourteen lot categories. The gavel falls at a fixed value of the score, $0.0450$ (SD $0.0038$), and not at a fixed value of money. Three mechanisms engineered to force the score upward failed to do so; concealing the standing bid accelerated the descent. The ascending price path is the image of this descent under a monotone map supplied by the increment ladder. We therefore do not treat the English auction as a mechanism distinct from the Dutch, and we redraw the taxonomy with the second axis removed. Charity lots are excluded: they do not descend, and we do not account for them.