Vocabulary breadth and depth

Vocabulary knowledge can be defined as knowledge of word meanings. However, because this knowledge can be variable, we need to distinguish between vocabulary breadth and vocabulary depth. Both vocabulary breadth and vocabulary depth are important for reading success, in different but overlapping ways.

Vocabulary breadth refers to the absolute size of a person’s vocabulary: all the words they’ve heard before or have some familiarity with. A person may understand, but not actively use all these words. (Words that are understood make up a person’s receptive vocabulary, while words that are used form part of their expressive vocabulary.)

Vocabulary breadth is important for both regular and irregular word reading. In the case regular words, children form expectations about how words they know might be spelled and this allows them to be read more rapidly. Having a wide vocabulary helps children to use set for variability or mispronunciation correction strategies to accurately read irregular words.

Vocabulary depth refers to the quality of the entry recorded against a particular word in a person’s mental dictionary (or lexicon). Words which are more deeply known will have richer entries and more connections to other words in the mental lexicon (e.g., to synonyms, antonyms or words that occur in similar contexts). They will be words a person can actively use.

Vocabulary depth contributes to reading comprehension. Words are stored in an interconnected network in our minds. This means that when we recognise a word (e.g., ‘fox’), we activate both knowledge about that individual word and knowledge of related words, concepts, facts and memories that we have connected to that word (e.g., ‘hunt’, ‘wild’, ‘red’, ‘sly as a fox’). It is this rich, interconnected knowledge base (or our vocabulary depth) that drives good reading comprehension.