preterite vs imperfect

express actions or states viewed by the speaker as completed

preterite

express beginning or end of a past action

preterite

narrate a series of past actions

preterite

describe an ongoing past action without reference to beginning or end

imperfect

to express habitual past actions

imperfect

describe mental, physical, emotional states/conditions

imperfect

to tell time

imperfect

using them together

imperfect: describes what was happening

preterite: describes action that interrupts the ongoing activity