This paper reports on patterns of verb choice in identifying relational clauses (e.g. ‘X is Y, Y is X’) in English technical manuals. While it is obvious that specific lexical verbs will feature in identifying clauses of different functions, e.g. mean (defining), call (naming), exemplify (exemplifying), less transparent is the distribution of these more specific verbs and the general or neutral verb be. The findings suggest that verb choice in (technical) identifying clauses is strongly associated with the degree of equivalence constructed between the two central nominal groups in the clause (the Token and Value). Equivalence relations are one-to-one (rather than one-to-many) and exhaustive (rather than semantically open). Major grammatical influences on equivalence include nominal group structure, ergativity of the clause, and the inclusion of features (e.g. interpersonal, logical or textual) that undermine the privileging of an experientially homogeneous world-view. The results challenge the notions that be and specific verbs are interchangeable and that be is an unmarked choice. On the contrary, the data reveal that under certain conditions be is the more marked choice. The results have practical implications for teachers and students of English (in particular, students of English for Academic and/or Specific Purposes) as well as translators.