Kango verbs + に purpose

Most of the time i see kango verbs retaining their する in patterns like 図書館に勉強しに来ます But there are some instances like 公園へ散歩に行きます where する is omitted (it's 散歩に not 散歩しに)

For now I stick to using する with all the kango verbs due to uncertainty, but would like to know when it's ok to omit する?

It is not kango verb + に, it's noun + に.
散歩に行く (go for a walk)、買物に行く (go shopping) - here the particle に indicate the purpose of the action (= 行く)

Ah, i think i get it. 講堂へ講義に行く implies that i go to hear a lecture 講堂へ講義しに行く implies that i go to give a lecture. Thanks for clearing this out, @undrentide

講堂へ / に講義に行く also means "I go to give a lecture". 講堂へ / に受講に行く / 受講しに行く is used for "I go to hear a lecture". 講堂での講義に行く can mean both "to give a lecture" and "to hear a lecture", though.

The key is what the part of speech of the word preceding に is, not the meaning of it. See the followng examples.

パリにフランス語の勉強に行く。
パリにフランス語を勉強しに行く。

In the former example, 勉強 is a noun, therefore the possession の is used. On the other hand, を is used in the latter case since 勉強し is the -masu stem of a verb 勉強する. The meaning is the same in either case.

Toritoribe said:

The key is what the part of speech of the word preceding に is, not the meaning of it. See the followng examples.

Click to expand...

I see. Thanks Toritobe