[...] two tentatively recognized components of one and the same class shall be reduced to one component if they are conformal and not commutable. The test which this rule institutes, and which we call the ‘derivate test’, is prescribed in linguistic theory for each individual stage of the textual analysis, coordinately with the commutation test; the two texts in conjunction are necessary to deduce whether or not a given object is a semiotic.
- Hjelmslev (1961), a pag.112