It is assumed that potentially every (semantic) verb, noun, adjective and adverb (i.e. every complex node) has subcategorization requirements, expressed by its valency frame. Valency modifications (in the broad sense of the word) include all kinds of elements (dependency relations) that can modify a particular lexical unit (or rather a lexical unit in a particular meaning).

In the present section - and in the whole manual in fact - the term valency is used in its stricter sense: the term valency modifications is reserved for the inner participants (arguments) and so called obligatory free modifications (obligatory adjuncts) (for the descriptions of individual types of modification, see Section 2.1.1, "Criteria for distinguishing between inner participants (arguments) and free modifications (adjuncts)"). The valency (of a particular lexical unit) is recorded in the valency frame (which is in the valency lexicon, see Section 2.2, "Valency frames and the way they are recorded in the valency lexicon").

The general approach to valency (in PDT) is described in Section 2.1, "The PDT approach to valency". The description of the valency lexicon and the way the valency of individual parts of speech is captured in it are to be found in the two following sections (Section 2.2, "Valency frames and the way they are recorded in the valency lexicon" and Section 2.3, "Valency of individual semantic parts of speech"). The last section (Section 2.4, "Representing valency in the tectogrammatical trees") is devoted to the way valency is represented in the tectogrammatical trees.