What is the difference between ために and -masu root verb+ に?


What is the difference between these two grammar patterns?

>   1. わたしは 大学で **教えに** 英語を 習っています
>   2. わたしは 大学で **教えるために** 英語を 習っています
>




The biggest difference is in the **_range of usage_** that the two expressions
allow themselves.

「ために」 can be used in far more situations than 「に」 because:

> you can only choose from a handful of verbs for Verb B in 「[連用形]{れんようけい} of
> Verb A + **に** + Verb B」

whereas

> choices for Verb B in 「Verb A + **ために** + Verb B」 are unlimited.

Choices for **Verb A** , which expresses the purpose, are literally unlimited
for **both** structures.

Choices for **Verb B** in 「連用形 of Verb A + **に** + Verb B」, however, are
limited to those few that express "motion" such as
[行]{い}く、[来]{く}る、[連]{つ}れていく、[走]{はし}ってくる, etc.

> Your sentence #1 「わたしは[大学]{だいがく}で[教]{おし}えに[英語]{えいご}を[習]{なら}っています。」,

therefore, is incorrect and it makes nearly no sense. Why? Because 「習う」 is not
a motion verb and it cannot be placed there.

> Sentence #2 「わたしは大学で教えるために英語を習っています。」

is correct and it makes sense. It may not be 100% natural-sounding by the
native standard but we will not get into that. Point is it is a grammatical
sentence.

