Note 5 — PART I. A SYNOPSIS OF THE CASTILIAN LANGUAGE.
Reading edition
When the English imperfect tense, for instance, he united, may be expressed by he was uniting, or he used or was accustomed to unite, preserving the same sense, then it is to be translated by the imperfect tense in Spanish; thus—él unía. When that cannot be done, but it may be changed into did, then the preterit must be used—él unió. The same must be understood of all the verbs in the imperfect tense.