sostener

to hold, to hold upirregular-er verb

Where it breaks the pattern

sostener follows tener: irregular first-person form
sostener follows tener: e → ie when the stem is stressed
sostener follows tener: irregular preterite stem; the 1s and 3s endings are unstressed, so they carry no written accent
sostener follows tener: irregular future stem; the endings themselves are regular
sostener follows tener: conditional shares the irregular future stem
sostener follows tener: present subjunctive is built from the irregular yo form
sostener follows tener: imperfect subjunctive is built from the third-person preterite stem

Indicativo: sostener conjugation

	Presente	Pretérito	Imperfecto	Futuro	Condicional
yo	sostengo	sostuve	sostenía	sostendré	sostendría
tú	sostienes	sostuviste	sostenías	sostendrás	sostendrías
él / ella / Ud.	sostiene	sostuvo	sostenía	sostendrá	sostendría
nosotros	sostenemos	sostuvimos	sosteníamos	sostendremos	sostendríamos
vosotros	sostenéis	sostuvisteis	sosteníais	sostendréis	sostendríais
ellos / Uds.	sostienen	sostuvieron	sostenían	sostendrán	sostendrían

Participio: sostenido · Gerundio: sosteniendo

irregular form

Real sentences with the conjugated form highlighted, from Tatoeba, licensed under CC BY 2.0 FR.

Él sostenía una caja grande en los brazos.
He was holding a large box in his arms.
Tom sostuvo una pistola en la cabeza de Mary.
Tom held a gun to Mary's head.
Ella todavía sostiene su inocencia.
She still alleges innocence.

These verbs are tener with a prefix, and they inherit its irregular forms.