Cardinal numerals are usually considered to be a separate word class. On the assumption that cardinals are indeed lexical (and not functional) heads, this would imply that we need to distinguish a fifth category in addition to the four lexical categories that are standardly assumed: nouns, verbs, adjectives, and adpositions. However, it has long been claimed that cardinals have properties of other lexical categories. Heeroma (1948), for example, noted that cardinals are noun-like in the sense that they can denote objects such as specific numbers, grades, playing cards, etc. The cardinals in (6) are clearly nouns, since they are preceded by an article with no indication that they are followed by an empty noun. Moreover, the resulting phrases occur in typical nominal positions, e.g. as the complement of a preposition and a verb.

Heeroma also noticed that cardinals in prenominal position denote a (quantitative) property, which is why cardinals are sometimes classified as adjective-like elements. This raises the question of whether cardinals are nouns or adjectives. The second option seems less likely, since the examples in (7) show that cardinals do not exhibit the otherwise obligatory attributive inflection.

On the other hand, cardinals exhibit a wide range of noun-like features; cf. Corver (2001), Corver & Zwarts (2005) and Klockmann (2017:ch.4&5) for recent discussions. The examples in (6) show that cardinals can be preceded by definite and indefinite articles; example (8a) shows that they can also be preceded by quantificational determiners like elkeeach and iedereevery; (8b) illustrates the same for the demonstrative zoʼnsuch a.

That these determiners are associated with the cardinal and not with the noun minuten is clear from the fact that they can only be paired with a singular noun: elke/iedere minuutevery/each minute. We can therefore conclude that the internal structure of the bracketed noun phrases in (8) is [[elke/iedere/zoʼn cardinal] Nounpl] and not [elke/iedere/zoʼn [cardinal Nounpl]].

The examples in (6) have also shown that cardinals preceded by an article can occur in prototypical nominal positions such as the complement of a preposition or a verb. Corver & Zwarts (2005) provides further syntactic contexts in which both cardinals and nouns can be used. A first case is the approximative pattern iets van X in (9) with the meaning “something close to X”, where X can be either a numeral or a noun.

One might object that the direct object in (9a) could be assigned the internal structure [NP iets [PP van [NP dertig boeken]]], but this does not seem plausible because iets van dertig clearly has the same semantic function as ongeveer dertig in the paraphrase [[ongeveer dertig] boeken]. Furthermore, the examples in (10) show that the two noun phrases behave similarly in that they both allow the replacement of boeken by quantitative er; however, substitution of a nominal part of a PP-complement/modifier of a noun phrase is impossible, as shown in *Marie heeft een foto van drie honden en Jan heeft er [een tekening [van [twee honden]]] with the intended meaning “Marie has a photo of three dogs and Jan has a drawing of two dogs”.

It is important to note that the acceptability of (9a) overcomes the potential objection to the nominal analysis of cardinal numerals that the prenominal position is not accessible to noun phrases: the fact that ietssomething in iets van dertig is clearly nominal shows that this position is accessible to nominal modifiers.

Another syntactic context mentioned in Corver & Zwarts is the X-P-X sequence in (11), where X can be either a cardinal or a noun.

This section has presented syntactic reasons for assuming that cardinal numerals should be analyzed as nouns. There is also morphological evidence for the nominal status of at least some cardinal numerals (e.g. that they can be pluralized), which will be presented in the next section.