Dutro and Moran describe two types of words with the analogy of brick and mortar. Brick words are the important or key words, those that are bold-faced in a text or could be found in a glossary, while mortar words are utility words that connect and strengthen the core brick words. Mortar words include verbs connecting words like “therefore” or “but,” pronouns, prepositions and prepositional phrases, as well as general academic verbiage, such as “notice” or “compare.” While mortar words don’t stand on their own without brick words, they are necessary for constructing complete sentences. For example, the sentence “Rabbits are mammals, but frogs are amphibians” contains the brick words “rabbits,” “mammals,” “frogs” and “amphibians,” and the mortar words are “are” and “but.”