This document discusses the use of the preterite and imperfect tenses together in Spanish sentences. It provides formulas for sentences using the conjunctions "mientras" and "cuando" to join verbs. For "mientras", one verb can be preterite and the other imperfect, indicating interrupted or simultaneous actions. For "cuando", the second verb is typically preterite to mark a specific moment, though both verbs can occasionally be preterite. Examples are given to illustrate the meaning of different tense combinations.

1. Preterite vs.
imperfect
Using both in 1 sentence

2. Preterite—imperfect
formulas
0 The preterite and imperfect tenses are often used
together in the same sentence. There are a few typical
sentence/structure formulas that are easy to learn.
Two vocabulary words that are necessary to join two
past tense verbs in the same sentence are mientras
(while) and cuando (when). Notice that cuando does
not have an accent mark because it is not being used
as a question word.

3. Joining verbs with mientras
0 The conjunction mientras can be used to join two verbs in
the imperfect, or it can be used in sentences where one
verb is in the preterite and the other is in the imperfect.
The sentence will change meaning depending on the tense
of the verbs joined by mientras.
0 To indicate that two actions are occurring simultaneously
and are assumed to be ongoing, the conjunction word
mientras is used between two verbs, and both verbs will be
conjugated in the imperfect tense. It is necessary that
neither action interrupt the other for both verbs to be
conjugated in the imperfect tense.

4. Mientras examples
0 Sentence structure formula: Imperfect mientras
imperfect
0 Ellos secaban los platos mientras yo los lavaba.
They were drying the dishes while I was washing
them.
0 Mientras nosotros mirábamos televisión, ellos se
vestían. While we watched television, they got
dressed.
0 Ella leía el periódico mientras yo cocinaba. She read
the newspaper while I cooked.

5. Interrupted actions
0 When the verb following mientras is in the imperfect
and the other verb is in the preterite, the action of the
verb in the preterite interrupts the ongoing action of
the verb in the imperfect.
0 Sentence structure formula: Preterite mientras
imperfect
0 Samuel llamó mientras tú estudiabas.
Samuel called while you were studying.
0 It is acceptable to have mientras in between the two
verbs, or mientras may begin the sentence followed
by a verb in the imperfect, a comma, and a verb in the
preterite.

6. Joining verbs with cuando
0 The conjunction cuando is almost always followed by
the preterite tense because it indicates the specific
moment of the action of the verb that follows it. The
other verb in the sentence may be an ongoing action
that is interrupted by the preterite verb. In such cases,
the ongoing verb is in the imperfect tense.

7. Cuando examples
0 Sentence structure formula: Imperfect cuando
preterite
0 Alicia trabajaba cuando yo entré en la oficina.
Alicia was working when I entered the office.
0 Just like sentences using mientras, the sentence order can
be switched around, but the verb following cuando will be
conjugated in the preterite tense, regardless of where it is
placed in the sentence.
0 Sentence structure formula: Cuando preterite,
imperfect
0 Cuando yo entré en la oficina, Alicia trabajaba.
When I entered the office, Alicia was working.

8. Cuando with preterite
0 In some sentences, the conjunction cuando is used to join two
preterite verbs. This sentence structure indicates that the action
of both verbs was completed at the same time or that one was
the result of the other.
0 Sentence structure formula: Preterite cuando preterite
0 Carlos me llamó cuando él llegó.
Carlos called me when he arrived.
0 Yo grité cuando vi al fantasma.
I screamed when I saw the ghost.
0 Sometimes the same basic construction is reversed. Whenever
the conjunction cuando is the first word of the sentence, a
comma is placed between the two preterite verbs.
0 Sentence structure formula: Cuando preterite, preterite
0 Cuando él llegó, Carlos me llamó
When he arrived, Carlos called me.
0 Cuando vi al fantasma, yo grité.
When I saw the ghost, I screamed.