Compounding is a word formation process based on the combination of lexical elements (words or stems). In the theoretical literature, compounding is discussed controversially, and the disagreement also concerns basic issues. In the study of compounding, the questions guiding research can be grouped into four main areas, labeled here as delimitation, classification, formation, and interpretation. Depending on the perspective taken in the research, some of these may be highlighted or backgrounded.
In the delimitation of compounding, one question is how important it is to be able to determine for each expression unambiguously whether it is a compound or not. Compounding borders on syntax and on affixation. In some theoretical frameworks, it is not a problem to have more typical and less typical instances, without a precise boundary between them. However, if, for instance, word formation and syntax are strictly separated and compounding is in word formation, it is crucial to draw this borderline precisely. Another question is which types of criteria should be used to distinguish compounding from other phenomena. Criteria based on form, on syntactic properties, and on meaning have been used. In all cases, it is also controversial whether such criteria should be applied crosslinguistically.
In the classification of compounds, the question of how important the distinction between the classes is for the theory in which they are used poses itself in much the same way as the corresponding question for the delimitation. A common classification uses headedness as a basis. Other criteria are based on the forms of the elements that are combined (e.g., stem vs. word) or on the semantic relationship between the components. Again, whether these criteria can and should be applied crosslinguistically is controversial.
The issue of the formation rules for compounds is particularly prominent in frameworks that emphasize form-based properties of compounding. Rewrite rules for compounding have been proposed, generalizations over the selection of the input form (stem or word) and of linking elements, and rules for stress assignment. Compounds are generally thought of as consisting of two components, although these components may consist of more than one element themselves. For some types of compounds with three or more components, for example copulative compounds, a nonbinary structure has been proposed.
The question of interpretation can be approached from two opposite perspectives. In a semasiological perspective, the meaning of a compound emerges from the interpretation of a given form. In an onomasiological perspective, the meaning precedes the formation in the sense that a form is selected to name a particular concept. The central question in the interpretation of compounds is how to determine the relationship between the two components. The range of possible interpretations can be constrained by the rules of compounding, by the semantics of the components, and by the context of use. A much-debated question concerns the relative importance of these factors.