Hedde Zeijlstra's research focuses on the question of how and why languages can express a particular meaning in a particular way. There are two sides to this question.
First, how can the meaning of a sentence be derived from the sentence’s form? Following Frege’s well-known principle of compositionality, the meaning of a sentence comes from the meaning of its words and the way these words are structured. But quite often, a sentence contains either too much material (for instance, agreement morphology, such as ‘–s’ in ‘Mary sleeps’), which appears semantically superfluous, or too little: why does simply changing the word order turn a sentence into a question (‘John can run’ – ‘Can John run?’)?
Second, what is the range of variation that languages exhibit when it comes to expressing a particular meaning? Many languages use word order shifts to yield a question, but there is no language in which changing the word order makes a sentence negative. In order to express a negation, some special word or word part must be used. Why is that the case? What constrains the way in which meanings can be mapped to forms or the other way round?
These two questions determine the study of the interface between syntax and semantics, which is Hedde's major research area. In particular, he concentrates on the following four research interests.
NEGATION AND POLARITY
A universal property of natural language is that every language is able to express negation, i.e., every language has some device at its disposal to reverse the truth value of the propositional content of a sentence. However, the way in which languages express this negation can differ to quite a large extent. Not only do languages vary with respect to the form of negative elements, but the position of negative elements is also subject to cross-linguistic variation. Moreover, languages differ in terms of the number of manifestations of negative morphemes: in some languages negation is realized by a single word or morpheme, while in other languages it is realized by multiple morphemes. The syntax of negation is indissolubly connected to the phenomenon of (negative) polarity. In short, negative polarity items (NPIs) are items (such as ‘in years’ in English) whose distribution is limited to a number of contexts, which in some sense all count as negative. In his work Hedde has explored many phenomena related to negation and negative polarity.
AGREEMENT AND DOUBLING PHENOMENA
Many languages reflect meaning properties of some words on other words. For instance, in the sentence ‘we are happy’, the plurality of the subject is reflected in the verb choice ‘are’. Why is this? How does it work? Why is English relatively poor in this respect (there is very little agreement), whereas other languages are much richer in this respect or lack it altogether? How does agreement influence the syntax? Do, for instance, verbs with rich agreement stand in the same position as verbs with poor or no agreement? And are all instances of doubling the same? Is the word ‘nothing’ in dialects of English in which ‘I didn’t see nothing’ means ‘I didn’t see anything’ also a word that reflects agreement? Over the past years Hedde has formulated theory that attempts to reduce all doubling effects to syntactic agreement (known as the Flexible Formal Feature Hypothesis).
FEATURES AS GRAMMATICAL BUILDING BLOCKS
According to many syntacticians, words or word parts are not the cornerstone of syntax; the basic units of sentences are features. Features express particular grammatical information, such as [3rd person] or [singular]. Certain features are strongly connected to word meanings such as the [plural] feature of ‘cars’. Other features, however, are not, e.g., the plural feature on the verb ‘are’. This [plural] feature only reflects that the subject must be a semantic plural. Technically, the uninterpretable [plural] feature on ‘are’ must be checked against the interpretable [plural] feature on ‘we’ in a sentence such as ‘we are happy’. Apparently, features come in different varieties: interpretable and uninterpretable features, or maybe even better: independent and dependent features. These features take up a lot of Hedde's time. They make him wonder whether these are the only types of features that exist (yes, he’d say), and how they relate to each other: Must every uninterpretable feature be checked against an interpretable one (yes, he’d say again)? And what is the structural relation between these two?
CONSTRAINTS ON LINGUISTIC VARIATION
Given the above, it is the properties of words – namely features – that determine their behavior in sentences. One could say that syntactic rules reduce to checking the requirements of features on their words or word parts. But if so, what determines which kinds of features there are? And how can the absence or presence of particular features in particular languages be explained? Does that always remain constant or can it change over time? And if so, how? And why? Many syntacticians assume that the set of possible features is part of our innate knowledge (bluntly, we are born with them); Here, Hedde disagrees. His research tries to account for the fact that all grammatical features can be learned and that all constraints on them may follow from language-external causes. In recent work, Hedde has shown that such constraints do not affect the set of formal features, but also other linguistic facts, such as possible and impossible word orders.
Please have a look at Hedde's papers. Most of these questions are addressed there (though not always fully explained). If you would like to know more, feel free to send him a message via email or the contact form. He’d be very happy to explain further.