Learn French: Il est normal de se sentir triste parfois. - It is normal to feel sad sometimes.

When you want to say 'It is [adjective] to [do something]', the standard grammatical structure is Il est + adjective + de + infinitive. In everyday spoken French, you will often hear people say C'est normal de..., but Il est is the proper, slightly more formal way to write it.

Why is the word de necessary before se sentir?

In French, when you use an impersonal phrase like Il est normal (It is normal) and follow it with an infinitive verb, you must connect them with the preposition de. The rule for this lesson is exactly this pattern: Il est + adjective + de + infinitive.

Why is it se sentir instead of just sentir?

Sentir on its own usually means 'to smell' or 'to sense' something outside of yourself. When you want to talk about experiencing an emotion or a physical state (like feeling sad), you must use the reflexive verb se sentir. Since it follows the preposition de, the verb stays in its infinitive form.

Could I put parfois at the beginning of the sentence?

Yes! Adverbs of time like parfois (sometimes) are quite flexible in French. You could also say Parfois, il est normal de se sentir triste and it would mean exactly the same thing.