If a culture smelted a metal, then it had a distinct word for that metal. If a culture was unfamiliar with a metal, then it did not have a distinct word for that metal. If a culture smelted copper and bronze, then it had distinct words for copper and bronze. If a culture had a distinct word for a metal, then it smelted that metal.
Archaeologists are discovering a great deal about the Sals culture. For example, recent excavations have unearthed smelting furnaces and tools of smelted copper and bronze. There were distinct Sals words for copper and for bronze, but none for iron. Thus, the Sals did not smelt iron.
The conclusion drawn above follows logically if which one of the following is assumed?