Why is "de" in a phrase sometimes and not at other times?
Why is de in some phrases and not in other. Example
Es de manana
but
Es meliodis
5 Answers
As a Spanish native speaker, I believe the problem comes from the double meaning of the word "mañana"... It can both mean "tomorrow" or "morning"... In Spanish, if you say "Mi cumpleaños es mañana" means "My birthday is tomorrow", but when you say "Mi trabajo es de mañana" means "I work on mornings"... So, I deduce... When you say "es mañana" means the day, when you say "de mañana" means the time of the day...
I hope this could clarify your doubt!
Sorry, I think my answer would only confuse you. My answer concerned the many possible meanings of de, but.....
Actually, I only think that you are referring to how de is used in time expressions.
or why we would say Es mediodía., but in other situations say Son las dos de la mañana. They are both time expressions, but one uses de and one does not.
I'll leave it for someone else, as my mind is having trouble switching gears from explaining the possible meanings of de in your example.
Wow, what a question. It depends. For example... with the verb Tratar - to try to it is always followed by De and an infinitive verb "I try to eat" Trato DE comer.
but that's the tip of the iceberg, there are tons of meanings. You should probably listen to Gfreed above 
Siejaku is right.
Mañana is either a noun and an adverb.
noun 1. Morning. (f) 2. The part of the day from twelve o’clock at night to twelve o’clock at noon. (f)
adverb 1. Tomorrow. 2. Soon. 3. Expression of negation. 4. In time to come.
De mañana is a locution, an adverbial phrase, meaning early in the morning.
Salió al campo muy de mañana.
He left to the field early in the morning.
Oh my "de" has many uses.
The best way to see them all is to type "de" into the translate box at the top of this page.There you will see its definition, with many examples of its usage.
When you do it please read the entire page.
