The purpose of this dissertation is to account for the syntactic and semantic traits of Tłı̨chǫ modal clauses within a cross-linguistic typology of conditional clauses. This dissertation provides a comprehensive description and analysis of clauses that are introduced by nı̨dè, a Tłı̨chǫ word with cognates in many Dene languages. Clauses that are introduced by nı̨dè are modal adjuncts, which cover predictions about the future (future temporal adverbial clauses, when), hypothetical scenarios (conditional clauses, if) and generic or habitual generalisations about the world (restrictive clauses, whenever). I provide a unified account for all of these uses by showing that they are all in the realm of modality. I then hypothesise that nı̨dè is a complementiser which introduces a modal adjunct clause. I follow von Fintel (2006) and Kratzer (2012) and suggest that nı̨dè restricts a modal operator in its apodosis. This account explains apparent gaps in the Tłı̨chǫ grammar, and in particular within concessive adjunct clauses ('even though...'), which cannot be introduced by nı̨de, and attributes this mismatch to the difference between the factivity of concessive adjunct clauses on the one hand and modality in clauses introduced by nı̨dè on the other hand. I contrast this with concessive conditional clauses ('if.... even...'), which can be introduced by nı̨dè, and in which nı̨dè scopes over the concessive adverb kò (following Bennett, 1982, 2003). This work highlights the ways in which Tłı̨chǫ conditionals are different from, and similar to, previous cross-linguistic generalisations of conditionals. Conditionals in Tłı̨chǫ and other Dene languages differ from many accounts of conditionals, which focus on the role of the verbal form in communicating speaker attitudes about the hypotheticality of the proposition in the conditional (Iatridou, 2000; Karawani, 2014). In contrast, Tłı̨chǫ uses verb aspect inside clauses to indicate the action as complete or incomplete, much like in matrix clauses. Tłı̨chǫ speakers communicate their attitudes of the likelihood and hypotheticality of the proposition using other means, such as adverbs and evidentials. However, Tłı̨chǫ is also similar to other languages, in extending the modal nature of conditional clauses to a subtype of conditionals called premise conditionals, which communicate rhetorical devices and a variety of metatextual comments (Dancygier, 1993, 1999). This is unexpected, as I argue that nı̨dè must introduce a modal clause, whereas premise conditionals seemingly deal with facts. I argue that despite first impressions, Tłı̨chǫ premise conditionals are still within the realm of modality, as they are either used to express propositions that are not accepted as fact by the speaker, or are used to restrict a modal in the adjoined clause, much like hypothetical conditionals. The structure of Tłı̨chǫ premise conditionals is likewise similar to the structure that has been proposed in the past for other languages (Haegeman, 2003, 2010). / Graduate

In the Northern Athabaskan languages Tlicho Yatiì, Dene and Dene Dzage, copulas and auxiliary verbs are based on reflexes of two Proto-Athabaskan roots, *-LII and *-T’E’. I propose that in the first two languages, copulas with nominal complements show distributional differences that derive from a stage-/individual-level predicate distinction, and that historically, this distinction in the proto-language motivated the development of auxiliaries marking tense/aspect/mode distinctions solely from the copulas based on *-LII. Further, I propose that subsequent to this development, the original stage-/individual-level predicate distinction between the copulas disappeared in Dene Dzage, leaving the TAM markers as evidence of its historical existence. I provide support for these contentions with data from fieldwork in Tlicho Yatiì and from textual sources in all three languages, grounding the work in current theories of syntax and of temporal grammar.