In formal semantics, the squiggle operator is an operator which constrains the occurrence of focus. On one common definition, the squiggle operator takes a syntactic argument and a discourse salient argument and introduces a presupposition that the ordinary semantic value of is either a subset or an element of the focus semantic value of . The squiggle was first introduced by Mats Rooth in 1992 as part of his treatment of focus within the framework of alternative semantics. It has become one of the standard tools in formal work on focus, playing a key role in accounts of contrastive focus, ellipsis, deaccenting, and question-answer congruence.
The empirical motivation for the squiggle operator comes from cases where focus marking requires a salient antecedent in discourse which stands in some particular relation with the focused expression. For instance, the following pairs shows that contrastive focus is only felicitous when there is a salient focus antecedent which contrasts with the focused expression.
Another instance of this phenomenon is question-answer congruence, also known as answer focus. Informally, a focused constituent in an answer to a question must represent the part of the utterance which resolves the issue raised by the question. For instance, the following pair of dialogues show that in response to a question of who likes stroopwafel, focus must be placed on the name of the person who likes stroopwafel. When focus is instead placed on the word "stroopwafel" itself, the answer is infelicitous, as indicated by the # sign.
If instead the question is what Helen likes, the word "stroopwafel" will be the expression which resolves the issue. Thus, focus will belong on "stroopwaffel" instead of "Helen".
In the Roothian Squiggle Theory, is what requires a focused expression to have a suitable focus antecedent. In doing so, it also allows the focus denotation and the ordinary denotation to interact. In the alternative Semantics approach to focus, each constituent has both an ordinary denotation and a focus denotation which are composed by parallel computations. The ordinary denotation of is simply whatever denotation it would have in a non-alternative-based system. The focus denotation of a constituent is typically the set of all ordinary denotations one could get by substituting a focused constituent for another expression of the same type.
The squiggle operator takes two arguments, a contextually provided antecedent and an overt argument . In the above examples, is a variable which can be valued as 's focus antecedent, while itself could be the constituent [HELEN likes stroopwafel].
On one common definition, introduces a presupposition that 's ordinary denotation is either a subset or an element of 's focus denotation, or in other words that either or . If this presupposition is satisfied, passes along its overt argument's ordinary denotation while "resetting" its focus denotation. In other words, when the presupposition is satisfied, and .