Volume 24, Issue 3

Language change and biological evolution are sufficiently similar that biologists and linguists often face similar challenges in reconstructing paths of historical change connecting different species or languages. Tracing evolutionary change over time requires us to consider how shared features have been modified in different lineages since they shared a common ancestor, and this means we have to be able to establish meaningful comparability between traits. In some cases, we may wish to understand how the same ancestral trait has been modified in each lineage in response to different pressures. But in other cases, we may wish to ask whether particular traits often arise in response to certain circumstances. Biologists must therefore consider different reasons for similarities between species, and choose to compare those traits that are relevant to the story they want to tell. To reconstruct histories of change, we need to compare homologous traits (those similar due to shared ancestry). But comparing analogous traits (independently derived but similar traits) highlights how separate evolutionary lineages can find similar solutions to common problems. I will illustrate the importance of comparability in constructing evolutionary explanations using one of the more obscure yet fascinating examples of Charles Darwin’s scientific researches, his multi-volume taxonomic treatise on barnacles. Darwin faced the challenge of how to explain the evolutionary trajectory of unique and highly modified traits that appear to have no equivalents in related taxa. He did this by tracing the development of unique traits within growing individuals, looking for variation in these strange adaptations between individuals, and comparing them across species that varied in their degree of modification from their ancestor. Using meticulous observations to establish comparability, even in such an incomparable animal as the barnacle, he could reconstruct plausible evolutionary explanations for even the most bizarrely modified traits, such as the presence of parasitic males and the invention of the cement that sticks barnacles to rocks, boats and whales. Nowadays, scientists increasingly rely on DNA evidence to trace evolutionary paths, which brings both advantages and challenges in establishing comparability. Even if you, like most people, are not particularly interested in barnacles, Darwin’s underappreciated taxonomic work is a surprisingly good place to go to if you want to think about the issue of comparability and why it matters to understanding evolution.

It is hard to define structural categories of language (e.g. noun, verb, adjective) in a way which accounts for linguistic variation. This leads Haspelmath to make the following claims: i) unlike in biology and chemistry, there are no natural kinds in language; ii) there is a fundamental distinction between descriptive and comparative linguistic categories, and; iii) generalisations based on comparisons between languages can in principle tell us nothing about specific languages. The implication is that cross-linguistic categories cannot support scientific induction. I disagree: generalisations on the basis of linguistic comparison should inform the language sciences. Haspelmath is not alone in identifying a connection between the nature of the categories we use and the kind of inferences we can make (e.g. Goodman’s ‘new riddle of induction’), but he is both overly pessimistic about categories in language and overly optimistic about categories in other sciences: biology and even chemistry work with categories which are indeterminate to some degree. Linguistic categories are clusters of co-occurring properties with variable instantiations, but this does not mean that we should dispense with them: if linguistic generalisations reliably lead to predictions about individual languages, and if we can integrate them into more sophisticated causal explanations, then there is no a priori requirement for a fundamental descriptive/comparative distinction. Instead, we should appreciate linguistic variation as a key component of our explanations rather than a problem to be dealt with.

Linguistics, and typology in particular, can have a bright future. We justify this optimism by discussing comparability from two angles. First, we take the opportunity presented by this special issue of Linguistic Typology to pause for a moment and make explicit some of the logical underpinnings of typological sciences, linguistics included, which we believe are worth reminding ourselves of. Second, we give a brief illustration of comparison, and particularly measurement, within modern typology.

This article sets out a conceptual framework and typology of modality effects in the comparison of signed and spoken languages. This is essential for a theory of cross-modal typology. We distinguish between relative modality effects, where a linguistic structure is markedly more common in one modality than in the other, and absolute modality effects, where a structure does not occur in one of the modalities at all. Using examples from a wide variety of sign languages, we discuss examples at the levels of phonology, morphology (including numerals, negation, and aspect) and semantics. At the phonological level, the issue of iconically motivated sub-lexical components in signs, and parallels with sound symbolism in spoken languages, is particularly pertinent. Sensory perception metaphors serve as an example for semantic comparison across modalities. Advocating an inductive approach to cross-modal comparison, we discuss analytical challenges in defining what is comparable across the signed and spoken modalities, and in carrying out such comparisons in a rigorous and empirically substantiated way.