The Dutch suffix -heid, like -ness in English, forms abstract nouns from adjectives. In this paper, we explore the hypothesis that -heid gives rise to two kinds of abstract nouns: on the one hand, nouns referring to concepts, and on the other hand, nouns referring to states of affairs. An examination of a corpus of newspaper Dutch reveals that the referential function of -heid is typical for the lowest-frequency words, most of which are neologisms. Conversely, its conceptual function is found predominantly among the highest-frequency words. Detailed investigations of the use of these two sorts of words in context showed that the high-frequency words tend to be less well anchored in their context than the low-frequency words, and that they pattern more as independent units. Our data argue against the view that productive word formation goes hand in hand with the absence of any storage of full forms in the mental lexicon. Instead, we claim that high-frequency formations with the productive suffix -heid are available in the mental lexicon, whereas low-frequency words and neologisms are produced and understood by rule