The adverbs siempre and nunca often cause confusion among learners; they can be followed by both the imperfect (cantaba) and the preterite (canté). Confusion arises partly because they can refer to a repeated event (siempre ≈ cada vez; nunca ≈ ninguna vez) or they can refer to an entire delimited time that we call 'always'/'never' (siempre ≈ en todo momento; nunca ≈ en ningún momento). [See also todos los días + imperfecto/indefinido].
-Siempre pensé/he pensado que era una mala idea — I always thought it was a bad idea [En todo momento]
→Siempre pensaba que iba a traerme un regalo, y nunca lo hacía — I always thought he was going to bring me a gift, but he never did [Cada vez/ninguna vez]
-Siempre supe que acabarías siendo policía — I always knew you would end up being a policeman [En todo momento]
→Yo siempre sabía cuando él iba a llegar — I always knew when he was going to arrive [Cada vez]
-Siempre estuvo a mi lado — She was always by my side [En todo momento]
→Siempre estaba a mi lado — She was always by my side [Habitualmente]
-Nunca vino a visitarme [En ningún momento]
→Nunca venía a visitarme [Ninguna vez]
-Nunca hubo nadie en esa casa [En ningún momento]
→Nunca había nadie en esa casa [Habitualmente]
