incapaz

Soy incapaz de mentirle a mi madre.

I am incapable of lying to my mother.

Se mostró incapaz de resolver el problema solo.

He proved unable to solve the problem on his own.

Estaba tan cansada que era incapaz de mantener los ojos abiertos.

She was so tired that she was unable to keep her eyes open.

Nos sentimos incapaces de ayudar en ese momento.

We felt incapable of helping at that moment.

Es incapaz de guardar un secreto.

He is incapable of keeping a secret.