Learn Hardcore Spanish (Spain): La autora asegura que una sonrisa puede ser más poderosa que un regalo caro. - The author assures that a smile can be more powerful than an expensive gift.

asegurar expresses a statement of fact or strong belief, so the subordinate clause uses the indicative mood. You’d only use the subjunctive after que if the main verb expressed doubt, emotion, desire or uncertainty (e.g. dudo que).

What does puede ser mean here and why not just es?

puede ser literally means “can be” or “may be,” indicating possibility. If you say es más poderosa, you’re presenting it as an absolute fact. Using puede ser softens the claim and suggests it often can be more powerful.

Why is poderosa feminine?

Adjectives in Spanish must agree in gender and number with the nouns they modify. Here, poderosa describes sonrisa (a feminine noun), so the adjective also takes the feminine form.

Why do we use más … que for comparisons and not más … de?

When comparing two things directly in Spanish, you use más + adjective + que (e.g. más grande que). You only use más de when referring to quantities or amounts (e.g. más de cinco libros).

Could I say un caro regalo instead of un regalo caro?

Grammatically yes, but placing caro before regalo puts extra emphasis on caro or sounds more literary. The neutral, everyday order is un regalo caro.

Why is there an una before sonrisa? Could we omit it?

In Spanish, you generally need an article before countable nouns, even when speaking in general terms. Una sonrisa means “a smile” as one example of many. Dropping the article (sonrisa puede ser…) would sound ungrammatical here.

What does caro mean here? Can’t we use costoso?

Caro means “expensive.” Costoso is a valid synonym, but caro is more common in everyday speech, especially in Spain. You could say un regalo costoso for a slightly more formal tone.