Decomposition of "Lo primero disculparme por no haberte podido escribir en el mismo día"

Question

This sentence was written to me by Spanish native from Madrid:

"Lo primero disculparme por no haberte podido escribir en el mismo día"

I completely understand the meaning of it. But have some misunderstandings in terms of grammar. So 3 questions:

1. "disculparme" - Am I correct that it is reflexive verb of disculparse? At first I thought it should be imperative "discúlpame", but then I thought what this person meant that she is not asking me to forgive her, but rather she figuratively "forgives herself". In English it would be "I apologise", but not "forgive me".

2. "por no haberte podido escribir" - how is it formed? What tense is it? Feels to me like an idiom. At least I would never be able to form this myself logically before.

3. "En el mismo día" - shouldn't it be just "El mismo día"?

Answer 1

There should be a comma between "lo primero" (the subject of the sentence) and the rest (the subject complement):

• Lo primero, disculparme por no haberte podido escribir en el mismo día.

Literally, this translates as:

• First thing, apologize for not having been able to write you back the same day.

We can imagine that "lo primero" is short for "lo primero que quiero hacer" (first thing I want to do). There is a copulative verb missing (that's why a comma is necessary):

• Lo primero (que quiero hacer) (ES) disculparme por no haberte podido escribir en el mismo día.

"disculparme" is a pronominal verb in the infinitive form. The person wrote an infinitive because the verb "be" is implicit: lo primero es discuparme (the first thing is to apologize). We use "disculpar" when we excuse somebody else, and "disculparse" for "apologize".

"no haberte podido escribir" is a verb phrase in the perfect infinitive form (in English, a perfect gerund is required because of the presence of the preposition, but in Spanish we use infinitive). A perfect form is used to refer to the past:

1. Lo primero es disculparme por no poderte escribir... (now or in the past) (The first thing is to apologize for not being able to write...)

2. Lo primero es disculparme por no haberte podido escribir... (in the past) (The first thing is to apologize for not having been able to write...)

Finally, both "en el mismo día" and "el mismo día" are correct. The latter might be a bit more colloquial and, therefore, more usual.