When I was attending formal classes in learning Korean, I once dropped the term ‘verb in infinitive form’ in our class. Our teacher is not using this term but rather emphasized on the base form of verb which cannot be used in a conversation unless transformed to end in ㅓ or ㅏ.
This post deals with particle that is attached to a verb in the infinitive form. I made a post about this, more than a year ago perhaps , when I was starting to learn Korean. The rule is base form of the verb + either ㅏ or ㅓ. Verb in the infinitive form can only end in these two hangul character, of course if the base form ends in ㅏ or ㅓ then there is no need to add another one.
The particle 서 (seo) is attached to the infinitive form of the verb. As I always keep on mentioning particles are pronounced without pause. It is as if the particle is part of the original word.
So how is this particle used? Most of the particles I learned functions as grammatical marker in the sentence like the subject particle 가/이 (ka/i) and object particle 을/를 (eul/reul). This time around, 서 added in a verb in the infinitive form denotes two meanings:
First is to show cause and result similar to English word so (incidentally the particle is 서 romanized as seo but pronounced as so just like the English word). Here is an example:
시간이 없어서 아침을 먹지 않았어요. (Shigani opseoseo achimeul meokji anasseoyo). 시간이 없어서 I did not have time so 먹지 않았어요 i skipped eating breakfast. Although the sentence direct translation is time i don’t have so breakfast i did not eat, the lack of time made me skip my breakfast. The lack of time being the cause and the result would be not eating breakfast.
The second use of this particle is to show sequence similar to ‘so as to’ or ‘did and then’. This way the sequence of event is emphasized. The 1st and 2nd clause usually has the same subject. Here is an example:
서울에 가서 한강을 봤어어요. (Seoure kaso hangangeul bowasseoyo). 서울에 가서 I did went to Seoul so as 한강을 봤어어요 to see Han River. The purpose is to go to Seoul and the result is being able to see Han River.
Note that in the two sentences, verbs to which 서 is attached are in the present infinitive form, its the verb at the end of the sentence that drives the tense. This is the same case as that of verb in -고 form the verbs to which it is attached is not tensed. So what I learned is that 서 is never compatible with past-infinitive or future-infinitive form of the verb.