Kaarle Makkonen's theory of legal reasoning is based on the logical primacy of an isomorphic relation between the two fact-descriptions compared, the one as given in a legal norm and the other as (possibly) existing in the world. Nonetheless, Makkonen nowhere gives a precise definition of what an isomorphic relation amounts to. He merely states that in an isomorphic situation the applicability of a legal norm to the facts of the case is "clear and patently evident" to the judge, since there exists a picture relation between the facts in a legal norm and the facts in the world. Such an isomorphic relation can be analysed by Ludwig Wittgenstein's picture theory of language, as outlined in his masterwork Tractatus Logico-Philosophicus. According to Wittgenstein, the world consists of facts, or states of affairs, i.e. of "things' or objects and predicates (qualities and relations) attached to them, and not of "things' or objects as such, taken in isolation. The internal categorial structure and the external configuration structure of reality, as conceived by Wittgenstein, is then analysed in light of Erik Stenius' excellent commentary work on Wittgenstein's Tractatus. Any set of facts or states of affairs that can be analysed as different sets of combinations of objects (entities, things) and their predicates (qualities and relations) Stenius calls an articulate field. An articulate field corresponds to a fact-constellation or fact-description in the legal context. Also, the issues of institutional facts and Alfred Tarski's semantic theory of truth are taken into consideration.