～しにいく

Go to do
ます verb stem + にいく

～しにいく means “go to do” or “will go to do”. It’s also sometimes translated as “go Xing”. It’s pretty straightforward, but it uses the ます verb stem.

Note: this pattern communicates the purpose of going. This に is a “purpose marker“, indicating the purpose of 行く.  

Examples

• のみに行く – Go to drink/will go to drink. (go (for the purpose of) drinking)
• としょかんに　べんきょうしにいく – Go to the library to go study. 
• なぐりにいく – Go to punch/Will go to punch
• ピザを食べに行く – Go to eat pizza.
• あいさつしに行く – Go to say hi. 

Other Travel Words

You can also use other travel words in place of 行く, but its less common:

• かれはあそびにきた – he came to play
• たべにもどった – Went back to eat. (probably won’t really say this though).

*These are about the only 2 words other than 行く you might hear. 

Note about ます Stem

The ます verb stem is essentially a noun (nominal verb) for conjugation purposes; so the pattern becomes Nounにいく。This makes the verb stem kind of similar in meaning to verb + の.