The definition of a linguistic category fulfills several purposes: It spells out the intension of the concept so one can associate it with more basic concepts. From a methodological point of view, it provides the criteria for the subsumption of a phenomenon under the category. In order to fulfill this function, the definition must be operationalized.

The operationalization of a definition has the following structure:

1. From the definition, a set of criteria is derived.
2. Each criterion is converted into a test which may be “mechanically” applied to candidates and whose outcome decides whether or not the candidate comes under the concept.
3. The test is applied to an example.

The mechanical application of the test is mentioned in quotation marks since few steps of linguistic method can directly be executed by a machine; most require some human understanding. Nevertheless, the required understanding must be based on concepts and operations which are either obvious or have their own definition.

The purpose of the operationalization, in turn, is twofold:

• It enables the reader to understand why and how the author subsumes certain phenomena under a concept.
• For the author, it ensures consistent application of the concept in question.

Consider the definition of terminative aktionsart as an example: It might run like this:

A verbal lexeme has terminative aktionsart iff it designates a type of situation that, while developing dynamically over time, has an inbuilt end point such that when this point is reached, the situation necessarily ends.

This is a hybrid definition. We will take its structural part (“verbal lexeme”) for granted and examine its semantic features. Even if the reader has the necessary background to understand the semantic part of the definition, he is not therefore enabled to tell for a given verbal lexeme whether or not it has terminative aktionsart. This is achieved by the operationalization of the definition.

From the definition, the following tests on terminativity can be derived:

1. Given a verbal lexeme V and the test frames
   1. X Ved for a minute/hour/day ...
   2. X Ved (with)in a minute/hour/day ...
   Then if V is unobjectionable in frame #a, but requires additional interpretive effort in frame #b, V is not terminative (but durative). If, on the contrary, V is unobjectionable in frame #b, but requires additional interpretive effort in frame #a, V is terminative.
2. Given a verbal lexeme V and the test frame
   • X is Ving. Consequently, X has Ved.
   Then if the inference spelled out in the test frame is valid, V is not terminative. If it is invalid, V is terminative.

Both tests yield the result that German brennen ‘burn’ is not terminative (but durative), while German verbrennen ‘burn down’ is terminative. Since this type of result corresponds to traditional usage of the concept, the two tests count as an operationalization of the concept ‘terminative’ and its definition.