Material Coherence

Material Coherence is the measured property by which a substance, structure, or claim is held to belong to the Tower rather than merely to occupy it. It is distinct from solidity, weight, and age, none of which it reliably tracks. A granite lintel may register low coherence; a rumour of a lintel may register high. The property is recorded in whole units of coherence, abbreviated c, on the scale established by the Settling of the Coherence Scale of year 41, which fixed the reference mass — one untouched ledger of the Second Recension — at 1,000 c and every subsequent reading by comparison against it.

A figure in coherence is not permitted to stand alone. The Office of Material Coherence maintains that a bare reading is "an opinion with a number attached" (Fourth Concordance, Annex 9), and requires that every published value be accompanied by the gauge, the floor, the season, and the name of the clerk who read it. Readings taken without all four are archived but uncited.

Origin and the Settling

Before the Settling, floors were catalogued by weight, a practice abandoned after the Winter of the Two Stairwells (years 38–39), when eleven catalogues recorded the same landing at eleven different masses because each had weighed it on a different storey. The discrepancy was never resolved, but the Bureau of Material Coherence was founded to ensure it would never need to be. Its first act was to declare weight a local phenomenon and coherence a portable one. The Bureau's seal was subsequently etched onto the Material Keystone, where it remains legible from the fourth gallery on clear days.

Coherence is now the standard predicate for admission to the stacks. An item rated below 200 c is shelved in the provisional ranges; below 50 c it is entered in the loose-leaf registers and is not bound. The Bureau of Material Assessment notes drily that binding a low-coherence item causes the stitching to outlast the pages, which "reads well in the inventory and poorly in the hand" (Assessment Circular 12).

Measurement

Readings are taken with the standardized Reconciliatory Gauges, of which four grades are in service. The gauges do not touch the item. The clerk holds the gauge at a distance of one arm's length and records the deflection of its brass leaf; the leaf returns a value in coherence, and the clerk records it twice. Where the two records disagree, the higher is retained and the lower is stamped superseded. No one has explained the grounds for this preference. It predates the Office of Material Coherence and is thought to be older than the Concordance of Reconciliatory Practice, which codified it at Article 6 without comment.

Gauges are recalibrated against the Keystone each Librarian of Coherence's accession, and on no other occasion. A clerk of the ninth provisional range, Alderis Vann, requested an intermediate recalibration in year 118 after a season of readings that struck him as "uniform to the point of discourtesy"; the request was granted, the recalibration performed, and the readings returned unchanged. Vann's grievance against the Office — that a measurement which never moves cannot be shown to measure anything — was entered in the register and has never been answered. The Office's position is that an unchanged reading is the strongest possible evidence of an unchanged material.

Borrowed Coherence and Conjuration

Items that have been assembled from parts catalogued on different floors frequently exhibit more coherence than the parts themselves. This excess is termed Borrowed Coherence, and it is the reason the Bureau of Material Coherence performs the initial calculation of it before anything provisional may receive a Material Coherence Attestation. The Office of Material Coherence endorses such calculations, subject to the Axiom of Material Coherence, which holds that no whole may claim coherence its least coherent part cannot be made to support. In practice the Axiom is interpreted generously upward and strictly downward, depending on which range is complaining.

The unsponsored appearance of coherent matter is catalogued as Material Conjuration and classified under Unattested Material Emergence in the Quarterly Review of Material Coherence. The phrase is chosen to avoid the word new, which the Directorate of Archival Coherence objects to on the grounds that everything is new to somebody. See the Material Coherence Attestation (MCA-57) for the longest-running disputed case.

Scholarly disagreement

The principal dispute concerns whether coherence resides in the object or in the reading. The Guild of Applied Coherence holds the former: coherence is a material's own quality, and the gauges merely report it. The Chamber of Dimensional Coherence holds the latter, and cites the Third Concordance against the Guild — "a quality is a record of a quality, and the second is the one we keep" (Annex 2). The Bureau of Material Coherence has declined to adjudicate, noting that both positions produce identical readings and that the dispute is therefore "not presently expensive."

"Let the leaf fall where it lists; the ledger does not require the leaf to understand it."

— Seventh Concordance, Annex 1

A minor controversy of longer standing concerns the term's spelling in the older register, where cohesion appears throughout. The Office of Material Coherence attributes this to a copying fault in the Third Concordance; the Bureau of Material Cohesion, whose continued separate existence is tolerated, attributes it to the truth. The two offices exchange correspondence once a decade and have not reconciled.

Prohibitions and maintenance

Gauges may not be carried below the fortieth gallery unaccompanied, as the leaf has been known to swing without cause and the readings are consequently disputed. Clerks are further reminded that no gauge, however high its reading, may be used as a paperweight on any surface of coherence below 600 c, a rule entered without explanation after the incident at the Settling and never rescinded.

The Axiom of Material Coherence and The Principle of Material Coherence remain in force concurrently, though they contradict each other on the treatment of composite items. The Librarian of Coherence has ruled that both are to be cited, in the order that flatters the item. This ruling is itself uncatalogued.