Section 18.1.1.2 has shown that indefinite noun phrases are typically used to introduce new entities into domain D or to allow the speaker to be less specific than he could be. What we did not discuss is that an indefinite noun phrase like een concerta concert can have at least two readings: either it has a specific reading, in which case it refers to a particular identifiable concert, or it has a non-specific reading, in which case it can refer to any entity that has the property of being a concert. In many contexts it is difficult to distinguish between these two readings. Consider example (29). The speaker of this utterance may or may not know which concert Jan is going to next week: in the first case the noun phrase een concert is specific, referring to a particular concert that is identifiable by the speaker but not by the hearer, and in the second case it is non-specific, referring to a concert that is not identifiable by either the speaker or the hearer.

The distinction is rather vague in (29), but can be made clearer in other contexts. First, consider example (30a), which involves the modal verb willento want. If we are dealing with a specific indefinite noun phrase, the speaker is actually claiming that there is a concert next week and that he wants to go there (the so-called de re reading). So a natural continuation of the discourse would be the assertion that the speaker will try to get a ticket, as in (30b). If, on the other hand, we are dealing with a non-specific noun phrase, the speaker is not claiming to go to a particular concert and may not even know if there is a concert next week (the de dicto reading), and he could continue by saying that he will see if there is anything interesting going on next week, as in (30b').

Other contexts in which the two readings of indefinite noun phrases can be easily distinguished involve universal quantification. Consider example (31), which involves the universally quantified time adverb altijdalways. If it is a non-specific indefinite noun phrase, the sentence expresses that there is always one or another horse in the meadow. On the other hand, if the noun phrase is specific, it means that there is always the same horse in the meadow.

The difference between specific and non-specific readings has been treated in several ways in the literature. The more or less traditional one describes the difference in terms of scope interactions (e.g. May 1985). It is assumed that the indefinite article is actually an existential operator, and that the ambiguity that arises is due to the fact that this operator can take different scopes with respect to the modal/universal operator expressed by the modal verb or the universally quantified expression. The specific reading occurs when the existential operator expressed by the indefinite article takes scope over the other operator in the sentence, as in the (a)-examples in (32); the non-specific reading occurs when the existential operator is within the scope of the other operator, as in the (b)-examples.

According to others (e.g. Hornstein 1984), the difference is not related to the scope taking properties of the existential quantifier, but to the nature of the noun phrase itself. If the noun phrase is non-specific, it acts as an existential quantifier in the scope of the modal/universal operator, as indicated in (32b&b'). If it is specific, however, it does not act as an operator, but as a constant, i.e. a specific indefinite noun phrase like een paard actually behaves in the same way as a noun phrase like een zeker paarda certain horse. We will not discuss here what the correct semantic treatment of the ambiguity of indefinite noun phrases is.

Finally, it should be noted that although definite noun phrases usually refer to a specific entity in domain D, they occasionally allow two readings comparable to the specific and non-specific readings of indefinite noun phrases. This is especially the case with noun phrases like de president van de VSthe president of the USA in example (33), the reference of which changes over time: this definite noun phrase can simply refer to a certain person who happens to be president of the USA at the time of utterance (the specific, de re reading), but example (33) is also felicitous if elections are taking place at the time of utterance, so that it is not clear who will be president of the USA next year (the non-specific, de dicto reading).

Something similar applies to examples such as (34). The specific reading of the definite noun phrase de bus arises in contexts where the speaker can expect the addressee to be able to identify the specific bus he is talking about, e.g. if the speaker comes from A and there is only one identifiable bus that goes from A to B. However, this example is also possible with a non-specific interpretation of the definite noun phrase de bus in contexts where the addressee cannot be assumed to be able to identify the actual bus that the speaker took (e.g. when there are many buses/routes going from A to B, or when the speaker has to change buses in order to get from A to B). In such cases, the definite noun phrase de bus is used to refer to the means of transport; cf. Section 18.1.4.1 for a more detailed discussion of such cases.