[...] the empirical data can never strengthen or weaken the theory itself, but only its applicability.
- Hjelmslev (1961), a pag.14

In the prolegomena to the theory, it is in the realistic side of the theory that we shall be interested – in the best way of meeting the requirement of appicability. This will be studied by an investigation of each feature that may be said to be constitutive in the structure of any language, and by an investigation of the logical consequences of fixing those features with the aid of definitions.
- Hjelmslev (1961), a pag.19