he can't
He can't understand it.
Eso es algo que él no puede hacer.
That’s something he can’t do.
Él no puede escribir en inglés sin cometer errores.
He can't write in English without making mistakes.
He can't read it.
Él no puede tener hambre, acaba de almorzar.
He can't be hungry, he just had lunch.
He can't buy a car.
Él no puede haber perdido sus llaves.
He can't have lost his keys.