cw (03/01/83)
A recent article postulated that the exception that proves the rule used the word "prove" to mean "test'; that is, an exception tested a general rule and thus proved the correctness of the rule. The usage was held obsolete except in this phrase. This is an unusual misconception; however, there are several similar ones and I would like to explain exactly what this phrase means. The phrase comes from old legal usage. If a law did not include exceptions (for example, "all livestock are to be taxed at a rate of one pence per head"), then it might be argued that the legislature might not have intended household dogs, say, to be included under livestock. However, if the law reads "all livestock, except dogs and chickens, shall be taxed...", then the legislature obviously considered possible exceptions and decided exactly what it wanted to tax and what it didn't. Hence, the fact that the legislature included the exceptions proves the general premises of the rule. This is an old legal rule and usually misused; try either to avoid it or to use it correctly. Charles