Blocking can be defined as the non-occurrence of some linguistic form, whose existence could be expected on general grounds, due to the existence of a rival form. *Oxes, for example, is blocked by oxen, *stealer by thief. Although blocking is closely associated with morphology, in reality the competing “forms” can not only be morphemes or words, but can also be syntactic units. In German, for example, the compound Rotwein ‘red wine’ blocks the phrasal unit *roter Wein (in the relevant sense), just as the phrasal unit rote Rübe ‘beetroot; lit. red beet’ blocks the compound *Rotrübe. In these examples, one crucial factor determining blocking is synonymy; speakers apparently have a deep-rooted presumption against synonyms. Whether homonymy can also lead to a similar avoidance strategy, is still controversial. But even if homonymy blocking exists, it certainly is much less systematic than synonymy blocking. In all the examples mentioned above, it is a word stored in the mental lexicon that blocks a rival formation. However, besides such cases of lexical blocking, one can observe blocking among productive patterns. Dutch has three suffixes for deriving agent nouns from verbal bases, -er, -der, and -aar. Of these three suffixes, the first one is the default choice, while -der and -aar are chosen in very specific phonological environments: as Geert Booij describes in The Morphology of Dutch (2002), “the suffix -aar occurs after stems ending in a coronal sonorant consonant preceded by schwa, and -der occurs after stems ending in /r/” (p. 122). Contrary to lexical blocking, the effect of this kind of pattern blocking does not depend on words stored in the mental lexicon and their token frequency but on abstract features (in the case at hand, phonological features). Blocking was first recognized by the Indian grammarian Pāṇini in the 5th or 4th century bc, when he stated that of two competing rules, the more restricted one had precedence. In the 1960s, this insight was revived by generative grammarians under the name “Elsewhere Principle,” which is still used in several grammatical theories (Distributed Morphology and Paradigm Function Morphology, among others). Alternatively, other theories, which go back to the German linguist Hermann Paul, have tackled the phenomenon on the basis of the mental lexicon. The great advantage of this latter approach is that it can account, in a natural way, for the crucial role played by frequency. Frequency is also crucial in the most promising theory, so-called statistical pre-emption, of how blocking can be learned.
Morphology, understood as internal structure of words, has always figured prominently in linguistic typology, and it is with the morphological classification of languages into “fusional,” “agglutinating,” and “isolating” proposed by the linguists and philosophers of the early 19th century that the advent of typology is often associated. However, since then typology has shifted its interests toward mapping the individual parameters of cross-linguistic diversity and looking for correlations between them rather than classifying languages into idealized “types” and to syntactically and semantically centered inquiries. Since the second half of the 20th century, morphology has been viewed as just one possible type of expression of meaning or syntactic function, often too idiosyncratic to yield to any interesting cross-linguistic let alone universal generalizations. Such notions as “flexive” or “agglutinating” have proven to be ill-defined and requiring revision in terms of more primitive logically independent and empirically uncorrelated parameters. Moreover, well-founded doubts have been cast upon such basic notions as “word,” “affix,” and the like, which have notoriously resisted adequate cross-linguistically applicable definitions, and the same has been the fate of still popular concepts like “inflection” and “derivation.” On the other hand, most theoretically oriented work on morphology, concerned with both individual languages and cross-linguistic comparison, has largely abandoned the traditional morpheme-based approaches of the American structuralists of the first half of the 20th century, shifting its attention to paradigmatic relations between morphologically relevant units, which themselves can be larger than traditional words. These developments suggest a reassessment of the basic notions and analytic approaches of morphological typology. Instead of sticking to crude and possibly misleading notions such as “word” or “derivation,” it is necessary to carefully define more primitive and empirically better-grounded notions and parameters of cross-linguistic variation in the domains of both syntagmatics and paradigmatics, to plot the space of possibilities defined by these parameters, and to seek possible correlations between them as well as explanations of these correlations or of the lack thereof.
The morpheme was the central notion in morphological theorizing in the 20th century. It has a very intuitive appeal as the indivisible and invariant unit of form and meaning, a minimal linguistic sign. Ideally, that would be all there is to build words and sentences from. But this ideal does not appear to be entirely adequate. At least at a perhaps superficial understanding of form as a series of phonemes, and of meaning as concepts and morphosyntactic feature sets, the form and the meaning side of words are often not structured isomorphically. Different analytical reactions are possible to deal with the empirical challenges resulting from the various kinds of non-isomorphism between form and meaning. One prominent option is to reject the morpheme and to recognize conceptually larger units such as the word or the lexeme and its paradigm as the operands of morphological theory. This contrasts with various theoretical options maintaining the morpheme, terminologically or at least conceptually at some level. One such option is to maintain the morpheme as a minimal unit of form, relaxing the tension imposed by the meaning requirement. Another option is to maintain it as a minimal morphosyntactic unit, relaxing the requirements on the form side. The latter (and to a lesser extent also the former) has been understood in various profoundly different ways: association of one morpheme with several form variants, association of a morpheme with non-self-sufficient phonological units, or association of a morpheme with a formal process distinct from affixation. Variants of all of these possibilities have been entertained and have established distinct schools of thought. The overall architecture of the grammar, in particular the way that the morphology integrates with the syntax and the phonology, has become a driving force in the debate. If there are morpheme-sized units, are they pre-syntactic or post-syntactic units? Is the association between meaning and phonological information pre-syntactic or post-syntactic? Do morpheme-sized pieces have a specific status in the syntax? Invoking some of the main issues involved, this article draws a profile of the debate, following the term morpheme on a by-and-large chronological path from the late 19th century to the 21st century.