The diachronic interpretation of the grammaticalization cline implies a direction, as illustrated by the > symbols between points on the cline proposed by Hopper and Traugott (2003: 7), which is known as the unidirectionality hypothesis. Grammaticalization is often described as a unidirectional process. Elements tend to develop from less grammaticalized to more grammaticalized, and the converse is rarely observed (Hopper and Traugott 2003: 99-139, Haspelmath 2004, Börjars and Vincent 2011). Grammaticalization is known to involve phonological reduction (sections 2.2.1 and 3.2) and semantic bleaching (sections 2.2.1 and 3.3), which are processes that tend to be unidirectional as well. The present section discusses possible explanations in favour of the hypothesis that grammaticalization is primarily a unidirectional phenomenon.
Two decades ago, Haspelmath (1999: 1049) noted that very few explanations for this hypothesized unidirectionality had been put forth. His proposal draws on Keller’s application of the invisible hand theory to linguistics (Keller 1994), which posits that “language change is shown to result from the cumulation of countless individual actions of speakers, which are not intended to change language, but whose side effect is change in a particular direction” (Haspelmath 1999: 1043). According to Haspelmath (1999), the key concept that explains the unidirectionality of grammaticalization is the maxim of “extravagance”. The idea is that speakers want to stand out and be noticed, and that in order to do so, they need to innovate. This leads individual speakers to come up with novel ways of expressing common grammatical concepts.
An example given by Haspelmath (1999: 1057) is using by means of instead of with. In this framework, being innovative and noticed is equated with being socially successful. An important note is that this notion of extravagance is not necessarily specific to grammaticalization (and neither is the rest of Keller’s (1994) invisible hand theory). Extravagance itself is not sufficient to lead to change, and extravagant forms must be adopted by other speakers and spread. This is why frequency of use is also a required criterion for the raise of new grammatical forms. More recent work by Bybee (2011: 77) views increasing frequency of use as the central explanation for the unidirectionality of grammaticalization. Increases in the usage frequency of a linguistic element tends to be linked to phonological reduction (see sections 3.1 and 3.2 on frequency and phonological reduction). According to Bybee (2011), when frequency of use ceases to increase (or even decreases), the changes that have taken place do not revert back to their former states.
Several scholars have also used Chomsky’s (1995) Minimalist Program in order to explain the unidirectionality of grammaticalization. Roberts and Roussou (2003: 202-218) claim that grammaticalization involves the “upwards” reanalysis of lexical material in a hierarchically organized syntactic structure. This means that the type of reanalysis involved in grammaticalization concerns items that move upwards in syntactic trees. This direction is explained by the need for structural simplification and the avoidance of syncretism, which is related to language acquisition and the learning of grammar by new generations (Roberts and Roussou 2003: 202-205). Newer generations do not necessarily have access to the former lexical interpretation of an item that has grammaticalized and viewing it as exclusively belonging to the higher categories (in the sense of elements higher in the syntactic structure) is a simpler interpretation. The idea of syntactic direction is also explored in van Gelderen (2004: 17-37) who offers “economy principles” that describe syntactic change in a similar fashion, where lexical items tend to move up the syntactic tree by becoming syntactic heads. Further discussion and limitations of these generative approaches can be found in Börjars and Vincent (2011: 174-175).
Jäger and Rosenbach (2008) have proposed another explanation for the unidirectionality of grammaticalization which relies on the cognitive mechanism of asymmetric priming. Asymmetric priming is the phenomenon by which one idea strongly primes (i.e. evokes) another idea, but not vice-versa. For instance, the word hunter strongly primes the word rifle, but conversely rifle does not necessarily strongly prime hunter. According to Jäger and Rosenbach (2008), less grammaticalized items tend to prime the more grammaticalized ones, but not vice-versa, which explains why developments tend to go from lexical to grammatical. However, Jäger and Rosenbach (2008) is a programmatic paper and empirical investigation of the phenomenon has highlighted unexpected results.
Hilpert and Correia Saavedra (2018) compared the priming of lexical and grammatical counterparts of the same words. For instance, the word back can refer to a part of the body (i.e. it’s lexical counterpart) or be used in a more abstract way to mark opposite directionality when used with verbs such as come back (i.e. it’s grammatical counterpart). Hilpert and Correia Saavedra (2018) investigated whether such lexical uses primed the grammatical ones within the same sentence (e.g. Yesterday my back was hurting when I came back home), and vice-versa (He was turning back and fell flat on his back), using a maze-task design (Forster et al. 2009). Their results show that lexical elements do not prime their grammatical counterparts as one would expect given Jäger and Rosenbach’s (2008) predictions. In fact, the opposite effect is observed, namely that lexical elements hinder the processing of their
grammatical counterparts (i.e. negative priming). This might be attributed to a phenomenon known as “horror aequi” (Rohdenburg and Mondorf 2003), which refers to the fact that speakers tend to dislike the use of the same form within a short time, especially when it has different meanings. Despite these findings, more empirical work needs to be done to support those results, and asymmetric priming remains a possible explanation for the unidirectionality of grammaticalization. Indeed, Hilpert and Correia Saavedra (2018) relied on comprehension only and did not involve production, which could show different tendencies. Further discussion of the asymmetric priming hypothesis can be found in Baumann and Sommerer (2018), who developed a mathematical population-dynamic model to investigate links between asymmetric priming and grammatical change.
In sum, there are various different explanations regarding the reasons why grammatical changes tend to be unidirectional.3 It seems plausible that several of these explanations can be correct at the same time, as there is no reason to believe that unidirectionality has to be accounted for by only one. Furthermore, most of these explanations acknowledge the central role of speakers in the processes of grammatical change, at the level of the individuals (e.g. extravagance, priming mechanisms), or at a more collective level (e.g. frequency of use, generational learning). While the strong tendency for grammatical change to be unidirectional is rather commonly accepted, there is more divergence regarding the existence of change going in the opposite direction, namely the phenomenon known as degrammaticalization.
There are researchers who are critical of the hypothesized unidirectionality of grammaticalization (e.g. Campbell and Janda 2001, Campbell 2001b, Janda 2001, Joseph 2001, Joseph 2011). One of their criticisms is that unidirectionality is “built into the definition of grammaticalization” (Campbell 2001: 124), since it is defined as a development from lexical to grammatical (or from grammatical to more grammatical). A consequence is that any observation that does not fit within this definition can be considered as falling outside the scope of grammaticalization. A grammatical element developing into a lexical element would be viewed as an instance of lexicalization and thus be dismissed as not being a counterexample to the unidirectionality hypothesis. According to this view, the problem is that unidirectionality is “not an empirical hypothesis that can be tested, but an artifact of the definition itself” (Campbell 2001: 124). While this criticism is certainly valid to some extent, it mostly relies on the idea that definitions of grammaticalization where unidirectionality is “built in” treat it as an absolute property, which is often not the case. It is possible to
3 A notable different approach to the question is Kiparsky (2012) who proposes a new definition of analogy
subscribe to the definitions presented in section 2.1, such as Hopper and Traugott’s (2001), while at the same time acknowledging the existence of cases of degrammaticalization as presented in section 2.5. The view adopted in this dissertation is that unidirectionality is a robust tendency as there are more concrete examples of developments from less to more grammatical (e.g. Givón 1971, Heine and Kuteva 2002) than the reverse.
Developing a way to quantify grammaticalization is a first step in addressing some of these criticisms, because it can be used to test whether there are tendencies for increases or decreases as will be shown in chapter 6. This would provide additional empirical support for unidirectionality, the lack of which was severely criticized in Campbell (2001). In addition, it also provides a way to analyse larger datasets, which could be used to provide more empirical data regarding the relationship between the different aspects of grammaticalization and how they relate to each other. In chapter 5, the links between the different grammaticalization variables involved in the models will also be discussed, which may also substantiate the claim that grammaticalization is a composite change, instead of an epiphenomenon as discussed in section 2.1.
Another point of criticism is that the claim that cases of grammaticalization are more common than cases of degrammaticalization has not been formally investigated empirically. Researchers assume that lexical to grammatical developments are more common, simply because they are more studied than their counterparts. This is how Janda (2001: 292-304) argues that counterexamples to unidirectionality are in fact not as infrequent as many scholars believe. There is presently no systematic study that tries to count whether there are more grammaticalization versus degrammaticalization cases, which means that these criticisms cannot be entirely dismissed. While this particular issue will not be considered in the subsequent studies, finding ways to quantify grammaticalization from a more computational and systematic way is a first step in doing larger-scale studies to address these issues regarding grammaticalization and degrammaticalization.