Lexical ambiguity is one of the most fascinating properties of language. The same form can have several meanings; these meanings may be unrelated homonyms (e.g., dog bark versus tree bark), or they may be related polysemes (e.g., run for office versus run a company). For decades, research has probed why languages tolerate ambiguity (e.g., Wittgenstein, 1958), and how the cognitive system resolves the challenges it poses for language comprehension (e.g., Johnson-Laird, 1987; Swinney, 1979). This article focuses on a relatively understudied aspect of polysemy. Specifically, we ask whether there are patterns that govern the process of sense extension in polysemy, how these can be quantified, and whether adult language users are sensitive to them.

The different senses of polysemous words are most commonly linked by two types of lexical construct. One such construct is metaphor, where different senses have an analogical relationship, because they refer to something that is similar in form, function, or behaviour (e.g., pig ‘animal’ and pig ‘dirty person’). Alternatively, senses can be linked through metonymy, a construct in which different senses have a logical relationship, such as action-agent, part-whole, container-content, or cause-effect (e.g., tin ‘metal’ and tin ‘object made of tin’). Importantly, metaphor and metonymy are both constructs that allow the creation of new words by extending the meanings of already existing words, thus bypassing the need to create new lexical forms (Gibson et al., 2019). Polysemy provides a highly efficient mechanism for lexical creativity, and it is therefore unsurprising that its use is widespread in natural languages (Srinivasan & Rabagliati, 2015). Moreover, since there is some evidence that meaningful relationships between senses facilitate the learning of new senses (Fang et al., 2017; Rodd et al., 2012), it may be that polysemy also provides a vehicle for efficient word learning.

Polysemy can also be characterised in terms of the regularity of the underlying construct. Consider, for instance, pig, wolf, and shark. These words all have a base meaning, ‘animal’ (SENSE 1), and another, less frequent meaning indicating a person: ‘dirty person’ for pig, ‘lonely person’ for wolf, and ‘aggressive person’ for shark (SENSE 2). Because many other words in English exhibit the same type of extension (bird, chicken, leech, sheep, etc.), the pattern ANIMAL → PERSON can be described as regular (see also Apresjan, 1974). On the other hand, if a semantic extension appears only in one polysemous word (e.g., ANIMAL → COMPANY as in unicorn ‘fantastic animal’/‘startup company valued at over 1 billion’), it can be considered irregular. Previous discussion of polysemy has sometimes gone further than a binary distinction between regular and irregular patterns (Barque et al., 2018; Copestake & Briscoe, 1995; Dölling, 2020; Nunberg, 1995; Nunberg & Zaenen, 1992; Pustejovsky, 1995); for example, the pattern PHYSICAL PROPERTY → PSYCHOLOGICAL PROPERTY (softness, solidity, volatility, …) intuitively seems more regular than the pattern ANIMAL → PERSON (pig, wolf, shark, …). However, to date, few attempts have been made to assess or quantify the graded nature of polysemy regularity.

There has been substantial interest in how the different types of lexical ambiguity influence language processing (for an overview, see Eddington & Tokowicz, 2015; Falkum & Vicente, 2015; and see also Duffy et al., 1988; Frazier & Rayner, 1990; Klepousniotou, 2002; Pylkkänen et al., 2006), but work investigating how the regularity of polysemy patterns influences processing is very limited. In terms of types of ambiguity, one of the critical findings in this literature is that the unrelated senses of ambiguous words (e.g., dog bark versus tree bark) must have separate representations in the mental lexicon, while the related senses (such as run for office versus run a company) must have overlapping mental representations (e.g., Brocher et al., 2018; Frisson, 2009; Frisson & Pickering, 1999; Rodd et al., 2002). Studies have also found a stronger relationship between senses related through metonymy (such as tin ‘material’ versus tin ‘object’) than between those related through metaphor (such as pig ‘animal’ versus pig ‘dirty person’; Klepousniotou & Baum, 2007; Klepousniotou et al., 2008; Klepousniotou et al., 2012; Lopukhina et al., 2018; Yurchenko et al., 2020). In terms of the regularity of polysemy patterns, some studies have investigated whether senses resulting from irregular extensions are processed differently from those resulting from regular extensions (Brocher et al., 2018; Rabagliati & Snedeker, 2013), while others have examined the extent to which polysemy patterns are shared across languages (Srinivasan & Rabagliati, 2015). However, these studies have tended to characterise different forms of polysemy in a categorical manner; for example, by associating regular polysemy with metonymy and irregular polysemy with metaphor (e.g., Apresjan, 1974; Brocher et al., 2018; Klepousniotou et al., 2012).

There have been various approaches to quantifying aspects of polysemy in a graded manner; however, most of these measures have focused on aspects of single words such as sense dominance (Gilhooly & Logie, 1980; Twilley et al., 1994) and sense uncertainty (e.g., Filipović Đurđević & Kostić, 2023) rather than properties of polysemy patterns such as regularity. To date, only one approach to quantifying polysemy regularity in a non-categorical manner has been developed. Srinivasan and Rabagliati (2015) asked 33 speakers of 14 languages to judge the extent to which 27 polysemy patterns found in English are also found in other languages. They found that patterns that had more similar senses across languages were also more generative, in the sense that novel senses that followed these patterns were judged as more acceptable. For example, in English, words like chicken and lamb can label both the animal and its meat (pattern ANIMAL → MEAT); this pattern is attested in many other languages and is thus highly generative. In contrast, while, in English, words such as tin and glass can denote both the material and the artefact made of this material (pattern MATERIAL → ARTEFACT), in many other languages examined in Srinivasan and Rabagliati (2015), the words denoting these materials did not denote the same artefacts (e.g., in French, étain denotes the same silvery-white metal the English word tin refers to, but, unlike tin, it cannot be used to refer to an airtight container made of tinplate, and, in Russian, unlike English, the word that refers to the material ‘rubber’ can also refer to a car tyre), and in other languages, this pattern was not present at all, suggesting that it is less generative. Critically, Srinivasan and Rabagliati’s approach to quantifying polysemy patterns was based on the notion of cross-linguistic regularity. One advantage of this approach is that it offers novel insights into why conceptual structure makes some sense relations easier to grasp than others, and hence, why particular polysemy patterns are attested across multiple languages. Yet their approach does not allow one to quantify the strength of specific polysemy patterns within a language. Moreover, because their metrics are based on the linguistic intuitions of a small number of informants for each language, the reproducibility of their results is difficult to attest. It is thus more desirable to quantify finer gradations of polysemy regularity using information that can be derived from corpora, yet, we are not aware of any research that has attempted to do that.

The research presented in this article therefore had two aims. Our first aim was to investigate how to quantify polysemy regularity in a graded manner and by means of corpus-derived metrics, focusing in this initial investigation on metaphor patterns that apply to nouns. We propose four potential metrics of regularity and describe the methods used to compute them. Our second aim was to test adults’ sensitivity to polysemy regularity using these four metrics. We tested adults’ capacity to understand new senses in an acceptability judgement task involving existing and novel polysemy extensions (e.g., ‘the knee of a mountain road’ derived from the BODY PART → OBJECT PART pattern). We then used our four metrics of regularity to assess whether the acceptability of these novel extensions was influenced by the degree of regularity of the polysemy patterns from which they were derived. In the following sections, we first describe the four measures of regularity that we developed and then report an experimental study in which we assessed speakers’ sensitivity to pattern regularity.

In this section, we first introduce four measures that can be used to quantify the degree of regularity of polysemy patterns and then use semantic information extracted from the WordNet corpus to compute these four measures for 15 polysemy patterns in English. These patterns were selected based on the previous research on polysemy (Apresjan, 1974; Brocher et al. 2016, 2018; Carston & Wearing, 2011; Klepousniotou, 2002; Klepousniotou et al., 2012; Lakoff & Johnson, 1980; Srinivasan & Rabagliati, 2015) as well as our professional knowledge.

We conducted an online experiment to assess (a) whether adults have sufficient knowledge of the polysemy patterns to be able to generalise from them; and (b) whether this knowledge is graded according to the different metrics of regularity described above. Our experiment was based on the notion that adults’ knowledge of a polysemy pattern should modulate the extent to which they accept new sense extensions from that pattern. When patterns are highly regular, adults should be more likely to accept new sense extensions than for less regular patterns. To test this hypothesis, we developed a semantic judgement task with semantic neologisms as experimental stimuli. These neologisms were existing words that were used in a new context in our experiment, thus in a different sense, such as the moustache of the broom for moustache (Bastuji, 1974; Renouf, 2013; Smyk-Bhattacharjee, 2009). We then measured the extent to which adults found the context sentences plausible. In the remainder of this section, we describe our stimuli, participants, and procedure. Materials, data, and analysis code for the experimental work are available at https://osf.io/uhy75/.

Although polysemy is a fundamental characteristic of language, it remains poorly understood. Linguists have often observed that sense extensions in polysemy follow patterns (Apresjan, 1974; Barque et al., 2018; Copestake & Briscoe, 1995; Dölling, 2020; Nunberg, 1995; Nunberg & Zaenen, 1992; Pustejovsky, 1995); however, to date, the regularity of these patterns has not been well characterised. In psycholinguistics, polysemy is often described in a categorical manner; for example, a word is described as ambiguous or unambiguous (e.g., Rodd et al., 2002) or as regular or irregular (e.g., Rabagliati & Snedeker, 2013). Likewise, because metonymy is often assumed to be more regular than metaphor (Apresjan, 1974), some researchers have associated regular polysemy with metonymy and irregular polysemy with metaphor (Brocher et al., 2018; Klepousniotou et al., 2012).

The results of our regularity analysis demonstrate that it is possible to quantify the regularity of English polysemy patterns in a graded manner. The wide variation in regularity highlighted in our metrics is inconsistent with a characterisation of metaphor as ‘irregular’ (cf. Brocher et al., 2018; Klepousniotou et al., 2012). Although some of our metaphor patterns had very low regularity, these were at one end of a continuum, with other patterns being of such high regularity that it was difficult to find non-existing sense extensions. This initial investigation does not allow us to comment on how metaphor and metonymy compare in terms of the regularity of the patterns that they instantiate, but it would be possible to conduct this investigation using the methods and metrics that we have developed. Likewise, while our study was limited to English, it should be possible to apply our methods to other languages to determine the extent to which particular patterns are more or less regular across languages. This work would enhance the robustness of Srinivasan and Rabagliati (2015)’s initial attempts to measure cross-linguistic regularity.

Our approach to quantifying polysemy regularity is similar to attempts to quantifying productivity in morphology. The concept of productivity is usually decomposed into availability (categorical) and profitability (numeric) (Bauer, 2001). A morphological process is available if it can be used to coin new words in a certain situation. For instance, -ness can form novel deadjectival nouns in contemporary English and is thus available, in contrast to -th. Profitability refers to how frequently an available process is used to coin new derivatives, either in the past or in the present production. Profitability can be based either on the number of existing words that are formed through a morphological process, or on the propensity of a morphological process to create neologisms synchronically. Thus, measures of productivity based on profitability have some similarities to our metrics of polysemy regularity. For example, the size of the morphological series is close to our R₁ measure, and Aronoff (1976)’s definition of productivity as a ratio between attested and theoretically possible words is close to our R₂ measure. Other conceptions of productivity are further apart, since they aim to measure the propensity of a morphological process to create new words rather than its rate of instantiation in a language (e.g., Baayen, 1992, 1994, 2009; Lindsay & Aronoff, 2013; Plag, 1999; Spencer, 2019). Equivalent measures of polysemy productivity (i.e., the extent to which each polysemy pattern is important in the renewal of the lexicon) could be determined in a future study.

Importantly, our research findings go beyond a new linguistic description. Our data show that our characterisation of regularity can predict human acceptability judgements of novel sense extensions. In our experiment, novel sense extensions based on more regular patterns were judged as more acceptable than those based on less regular patterns. Our interpretation of this finding is that language users’ experience with these patterns shapes their intuition regarding the acceptability of novel senses. The fact that this result holds particularly for metrics R₂ and R₄ suggests that it is not the number of times that a pattern is instantiated that is important, but rather the consistency with which words that have SENSE 1 also have SENSE 2. Our results do not allow us to differentiate between these two metrics (R₂ and R₄), because they are highly correlated for the patterns studied in our analyses (Figure 2); however, distinguishing whether regularity is best measured using a type-based or a frequency-weighted ratio could be an important avenue for future research.

Our data further show that speakers tend to link two senses with each other more easily when these senses have a high probability of association (i.e., when both R₂ and R₄ are high). One possible reason for this finding could be that polysemy patterns, like individual polysemes, are represented in the mental lexicon, and that the strength of their representations is modulated by pattern consistency. At the level of individual words, if many words exhibit a particular semantic relationship, words that share the same semantic relationship between their two senses could have a type of parallel organisation in the mental lexicon that favours rule-based semantic analysis. The presence of such representations could explain why speakers generalise some polysemy patterns more readily than others, and it would be worthwhile to test this hypothesis in the future. One might also draw a parallel with the dual-route models in morphology (Bertram et al., 2000; Pinker, 1999; Pinker & Prince, 1988), and consider whether the different polysemous meanings are learnt and stored, or whether they are inferred from the patterns of polysemy, or both.

It is important to recognise the limitations of this research. Our study was intended to provide initial evidence regarding the objective measurement of regularity of English polysemy patterns. However, our conclusions are necessarily limited by the small number of polysemy patterns included in the acceptability study. This limitation means that we cannot definitively determine whether the effect of regularity on acceptability judgements is scalar or categorical. Likewise, the strong positive relationships between type-based and frequency-weighted regularity metrics in this limited sample of polysemy patterns means that we cannot determine which of these metrics provides a superior description of regularity. It will be important for future studies to replicate our findings with more polysemy patterns that vary widely in terms of regularity. Similarly, while this study provides initial evidence for the psychological reality of polysemy regularity, pre-registered confirmatory studies are needed to establish this phenomenon more robustly.

Future research should also investigate the potential effect of concreteness on acceptability judgements. Because one of our patterns (PHYSICAL PROPERTY → PSYCHOLOGICAL PROPERTY) was characterised by an abstract SENSE 2, we created two types of ‘illegal’ sense extensions, one that was concrete (to match the other ‘illegal’ sense extensions) and one that was abstract (to match the SENSE 2 extensions for this pattern). Since we did not have a prediction about how concreteness might influence acceptability judgements, the observed results need to be treated with caution. However, there is an indication that abstract sense extensions may be judged as more acceptable than concrete sense extensions. If confirmed empirically, this observation may have important methodological implications in terms of the need for investigators to control the concreteness of foils in experiments of this nature. Furthermore, this issue raises interesting theoretical questions about why abstract words may be better able to take on new meanings than concrete words.

In summary, the research presented here has pioneered an approach for quantifying the regularity of polysemy patterns in a graded manner. We have demonstrated that this approach has psychological validity, and we hope that this work inspires new work investigating the influence of regularity on the learning, processing, and storage of polysemes in a more precise and nuanced way than has previously been possible under categorical conceptualisations. The approach documented here could be used to study how the consistency of polysemy patterns changes through the course of language development, and also how polysemy patterns vary across the world’s languages.