A spec that says adding a fixnum to a string produces a possibly-runtime error isn&#x27;t a type system, it&#x27;s just a particular instance behaviour. Types are by definition associated to terms in a language.<p>(That isn&#x27;t to say that that kind of runtime behaviour isn&#x27;t valuable or doesn&#x27;t provide (some of) the same functionality as a type system. But it&#x27;s not what the word &quot;type&quot; means).