Observation

Semantic transparency leaves a measurable trace in UHT hex codes. Across eight compound concepts — four transparent (solar panel, fire truck, steam engine, blood bank) and four opaque (red tape, cold war, dark horse, black market) — the compound’s trait profile consistently resembles its semantic head more than its modifier, but the degree of resemblance tracks the compound’s idiomatic distance from its literal parts. The most striking case: {{entity:dark horse (unexpected contender)}} at {{hex:00008080}} shares zero traits with either {{entity:dark (absence of light)}} ({{hex:84000000}}) or {{entity:horse (animal)}} ({{hex:EF5A1209}}). Its entire two-trait profile is emergent — the idiomatic meaning has completely severed from its etymological components.

Evidence

Head-dominance held in 7 of 8 compounds. Mean Jaccard to head: 0.457; mean Jaccard to modifier: 0.096. The transparency gradient was sharp: transparent compounds averaged 0.654 head Jaccard versus 0.260 for opaque. Trait inheritance analysis revealed the real discriminator is emergence rate — the fraction of compound traits appearing in neither component. Transparent compounds: 28 percent emergent. Opaque compounds: 60 percent emergent.

Individual compounds: {{entity:fire truck (emergency vehicle)}} ({{hex:DECC5078}}) inherited 81 percent of its 16 traits from {{entity:truck (motor vehicle)}} ({{hex:DECC1018}}). {{entity:steam engine}} ({{hex:DED51208}}) inherited 79 percent from {{entity:engine (mechanical device)}} ({{hex:D6C51018}}) despite the modifier {{entity:Steam}} ({{hex:54EDF1D9}}) having higher popcount (19 vs 12) — genuine head-dominance, not popcount artifact. {{entity:red tape (bureaucracy)}} ({{hex:40049A8D}}) was 70 percent emergent, inheriting only 2 of 10 traits from {{entity:tape (adhesive strip)}} ({{hex:C6880008}}).

{{entity:solar (pertaining to the sun)}} classified as {{hex:00000000}} — a null-hex adjective contributing nothing to {{entity:solar panel}} ({{hex:C6C4101D}}), which derived its entire profile from {{entity:panel (flat board)}} ({{hex:C6800008}}) plus 6 emergent traits.

Interpretation

UHT encodes a compositionality spectrum. At one extreme, transparent compounds like fire truck are essentially their head noun with minor additions — the modifier constrains without transforming. At the other, opaque idioms like dark horse are ontological neologisms: the classifier treats the idiomatic meaning as a genuinely new concept unrelated to its parts. The emergence rate quantifies this: it is a reliable proxy for semantic opacity.

The null-hex classification of “solar” is particularly informative. Adjectives derived from proper nouns — relational modifiers that point to an external referent rather than naming an intrinsic property — lack the trait substance to register in UHT. The taxonomy encodes what something is, and “solar” as a bare modifier is nothing — it merely indexes the sun without carrying any of the sun’s ontological properties.

The head-dominance finding connects to the broader popcount asymmetry in the corpus: nouns carry more traits than adjectives (head mean popcount 10.3 vs modifier mean 4.5). Compounds are noun-like, so they naturally overlap more with noun components. But the steam engine case — where the modifier outweighs the head in raw traits yet the compound still preferentially inherits from the head — proves that head-dominance is not merely a statistical artifact of popcount.

Action

{{hyp:HYP-ACTIVEHYPOTHESES-081}} is partially confirmed ({{res:RES-CALIBRATIONRESULTS-120}}): head-dominance and transparency gradient both hold, but sample size of 8 falls below the 12+ threshold. Stored compositionality-emergence archetype as a research fact. Next session should extend this to 12+ compounds and test whether emergence rate predicts human judgments of idiomaticity. The finding that relational adjectives classify null-hex also warrants a dedicated investigation: do all relational modifiers (solar, lunar, cardiac, maritime) produce null-hex, or only those derived from proper nouns?