Like many other languages, Dutch has quite a few modal adverbs/particles expressing the speaker's emphatically-positive attitude with respect to the truth of the expression's content. The words ZEKER, VAST, TOCH and WEL all share this property. ZEKER and VAST express, roughly, certainty or high probability of the propositional content, TOCH and WEL express, roughly, truth "for all that".

The application domain of these meanings is variable. For example, when used as modal adverbs in affirmative sentences, the words express the speaker's own claims of truth. When used as modal particles in questions, they express the speaker's expectations about the listener's affirmative reaction.

Another symptom of the typological similarity of these words is their facility of particle-clustering: various two-particle combinations and one three-particle combination (TOCH ZEKER WEL) are highly frequent. In clusters, one particle is dominant, which is apparent from the cluster's meaning and characteristic intonation pattern; the others are supportive.

In my lecture I will pay attention to similarities as well as differences within this group of adverbs/particles.

1) Semantics. Earlier (near-)identifications of the strong affirmative meanings of ZEKER and VAST, and of WEL and TOCH are refuted through a closer observation of the relevant facts. In spite of the above-mentioned common features, the meanings, and thereby the applicability in various types of discourse, of the members of both pairs present substantial differences. These observations can be accounted for by the assumption of basic meanings for each of the four words at issue, in all their modal uses: ZEKER = CONFIRMATION, VAST = STRONG BELIEF, TOCH = PERSISTENCE, WEL = DEFENCE. The various more specific interpretations of the words cannot be entirely reduced to these meanings plus the meanings of position, accent and intonation patterns (which are related to illocutionary force); they exhibit idiosyncratic aspects as well as systematic interaction effects (as mentioned in the second paragraph above). Some of these idiosyncratic aspects, however, may turn out to attributable to "suitability" for certain discourse applications rather than to linguistic properties of the elements themselves, as is the case with the alleged 'disdain' connotation of ZEKER as a modal particle. Nonmodal uses (only relevant to ZEKER and VAST) can also be analysed in terms of the assumed basic meanings; in some uses, however, the relation to these meanings is rather diffuse or still unclear.

2) Clustering. A systematic overview is presented of (im)possibilities and semantic effects of particle clustering in relation to various intonation patterns. The idiomatic combination VAST EN ZEKER (Flemish: ZEKER EN VAST) turns out to behave in a way similar to particle clusters: one meaning (of VAST) is dominant, in conformity with the intonation pattern ("tautology" and "twin formula" are, therefore, imprecise names for the figure of speech to which VAST EN ZEKER belongs).

3) (Im)possibility of accent and/or first position As is well known, there are exceptions to the general rule that modal adverbs can and modal particles cannot bear accent and occupy first sentence position. This suggests a not too strict separation between modal adverbs (proposition-modifying) and modal particles (illocution-modifying), rather a gradual transition. My analysis of Dutch adverbs/particles of truth strongly supports this idea. Although there is still much unclarity about this issue, my tentative ideas are the following. There are modal adverbs which resemble particles by expressing a very strong pragmatic appeal to immediate context. This prevents first position. ZEKER, used as a modal adverb, is an example of this phenomenon. Modal particles seem to constitute a continuum, running from purely speaker-oriented (and thereby adverb-like and accentable) to purely interactive (unaccentable). VAST is reanalyzed as representing the speaker-oriented side of this scale. ZEKER and WEL, used as modal particles, can represent both sides.