Lat. pro subjecta materia argument, Lat. subjectus, “adjacent, near”, materia “topic”.

The interpretative argument from the subject matter of the law requires that the text of a law or of a regulation be interpreted not absolutely but depending on the matters concerned, that is to say, the specific material topic and purpose of the law,S. Juridical arguments.

In the following case, the interpretation derived from the object of the law leads to the redefinition of the expression territory entirely covered by snow as meaning “places where the snow layer is sufficient for tracking game”, since the purpose of the law is the protection of game. The same expression would be defined in a very different way if its purpose were, for example, the regulation of off-piste skiing.

What is meant by, “territory entirely covered with snow”? If this condition were interpreted literally, the prohibition of hunting in snow would hardly ever produce any result. […] The purpose of the law is to prevent the destruction of game, but this destruction is not prevented if I hunt, out of the woods, on land where I can follow the track of the game, although the neighboring grounds are stripped of snow.
It is therefore of little consequence that the snow should be melted over an area of ​​one hundred acres of rocks or marshy land, if I go hunting on the nearby land which remains covered with snow. Is it true that, in our hypothesis, the object of the prohibition would be evaded, if we admitted a contrary interpretation? — Quite obviously yes. It is therefore necessary to agree with our opinion, since the word “entirely” used here is impossible to apply literally. It is therefore necessary to attribute to it only the meaning and the scope that it contains pro subjecta materia.
Thus I think that there is an offense whenever one is found hunting, outside the woods, on snow-covered ground, as long as one can track the game.
Renaissance Joseph Bonjean, [Code of Hunting], 1816.[1]

The subject matter corresponds to the intention of the law, itself determined with reference to the intention of the legislator, here to protect game. If the subject is indicated by a title, the argument of the subject matter of the law and the argument of the title of the law (a rubrica) converge to the same conclusion.

The argument of the subject matter of the law is quite different from the argument to the to the matter. The former refers to the content of a specific law, the later to the matter at issue in an argumentative situation.

[1] Renaissance Joseph Bonjean, Code de la chasse, vol. 1, Liège: Félix Oudard, 1816, p. 68-69.