The two endings sets, worked through in full
Regular preterite verbs take one of exactly two endings sets, decided only by whether the infinitive ends in -ar or in -er/-ir. -Ar verbs (modeled on hablar): hablé, hablaste, habló, hablamos, hablasteis, hablaron. -Er and -ir verbs share a single set (modeled on comer and vivir): comí, comiste, comió, comimos, comisteis, comieron; viví, viviste, vivió, vivimos, vivisteis, vivieron. There is no separate -er set and -ir set here, unlike the present tense, where the two conjugations split in the nosotros and vosotros forms (comemos/coméis versus vivimos/vivís).
Hablé con mi hermana ayer ("I talked with my sister yesterday"). Comimos en ese restaurante la semana pasada ("We ate at that restaurant last week"). ¿A qué hora llegaste? ("What time did you arrive?"). Every regular verb in the language slots into one of these two sets with no further variation; strong irregular preterites use their own unaccented endings, with -eron rather than -ieron in the j-stem group. For the verbs that do swap in a new stem, see the irregular preterite verbs breakdown.
Why the accents land on yo and él/ella/usted, and nowhere else
The hablar, comer and vivir examples have two accented forms: hablé/habló and comí/comió/viví/vivió, on the yo and él/ella/usted rows. That follows a general Spanish stress rule, not a special preterite-only exception. Spanish requires a written accent on a polysyllabic word stressed on its last syllable (a class called aguda) when that word ends in a vowel, or in -n or -s not preceded by another consonant. Per Real Academia Española's own reference on the general accentuation rules, that's the same rule that puts a tilde on words like comité, colibrí, and razón.
Monosyllabic forms follow a different rule: regular criar has crie and crio without tilde under current orthographic conventions. Hablé and habló are both stressed on their final syllable and end in a vowel, so the rule forces the accent. Hablaste, hablamos, and hablasteis are all llana, stressed on their second-to-last syllable, so none of them qualify, and hablaron is llana too, stressed the same way, so its final -n doesn't trigger an accent either. That's a different mechanism from the Spanish imperfect's accent rule, where the -ía endings take a tilde in every single form because of a hiato (a stressed closed vowel, here í, next to an open vowel), not because of where the stress falls. The conditional endings chart shares the -ía shapes but attaches them to the full infinitive. The verb tenses chart places preterite beside imperfect for side-by-side comparison. Which tense a Spanish speaker actually reaches for to describe a recent event, this preterite or the present perfect, isn't fixed either: it splits by region, with most of Latin America defaulting to the preterite for something that happened moments ago and most of Spain reaching for the present perfect instead.
Nosotros sometimes matches the present tense, and sometimes doesn't
The nosotros form of the preterite is spelled identically to the nosotros form of the present tense for -ar and -ir verbs, but not for -er verbs. Hablamos means both "we speak" and "we spoke," with no spelling or accent difference at all; vivimos means both "we live" and "we lived," for the same reason. Comemos ("we eat") and comimos ("we ate") don't share that overlap; the -er preterite nosotros form takes -imos, not -emos, so it stays distinct from its present-tense counterpart.
Context almost always resolves the -ar/-ir overlap for a listener, the same way English read is spelled identically in the present and past tense and gets sorted out by the sentence around it: Hoy hablamos con el gerente ("Today we talk with the manager") versus Ayer hablamos con el gerente ("Yesterday we talked with the manager"). A time word like hoy or ayer, or the surrounding verb tenses in the rest of the sentence, is what actually carries the distinction, not the verb form itself.
Standard hablaste and the different sources of final -s
A widespread nonstandard habit adds an extra -s to the tú preterite form: hablaste wrongly picks up an -s to become hablastes, comiste becomes comistes, and dijiste becomes dijistes. Many other finite tú forms end in -s (hablas, hablarás, hablabas, hablarías, hablaras), which makes the preterite the one tense where tú breaks that pattern with a bare -e or -iste ending. The extra -s is an analogy correcting for that irregularity, not a random typo, which is also why it shows up reliably across very different Spanish-speaking regions, not clustered in any single one.
Forms without final -s, such as vos hablaste, vos comiste and vos viniste, are preferred in standard voseo. The RAE also records an etymological voseo preterite with final -s, which generally receives negative social evaluation. The historical voseo ending and the analogical addition in tú should not be treated as identical in origin, even though the resulting forms can coincide. The extent of distinct voseo forms varies by region; it is not confined to the indicative present and commands.