Learn Hardcore Japanese: gakkou ni iku mae ni, watasi ha ie de kigaemasu. - Before going to school, I change clothes at home.

The first に marks the destination of 行く (“to go to school”). The second に is part of the time-expression ～前に (“before ~”). They look the same but serve different grammatical roles: one is a location/direction particle, the other makes 前 into “before.”

Why is the verb 行く in dictionary form before 前に instead of past tense or the te-form?

To express “before doing something,” Japanese uses the dictionary form of the verb + 前に. You do not use the past (e.g. 行った前に) or the te-form. So 学校に行く前に literally means before going to school.

Could I say 学校へ行く前に instead of 学校に行く前に?

Yes. Both に and へ can mark direction with 行く, though に is more commonly used for definite destinations. 学校へ行く前に is grammatically correct and means exactly the same.

Why is 家で used here instead of 家に?

The particle で indicates where an action takes place. Since 着替えます (“change clothes”) is an action happening at home, you use 家で. If you used 家に, it would imply movement toward home or simply existence at home, which doesn’t match the meaning.

Why is 私 marked with は instead of が, and could it be omitted?

は marks the topic of the sentence (“as for me…”). が would emphasize the subject in contexts introducing new or contrasting information. Here the speaker is simply stating a routine, so 私は is natural. You can also omit 私は entirely when it’s clear from context: 学校に行く前に家で着替えます still clearly means “Before going to school, (I) change clothes at home.”

Why is the verb 着替えます used, and how is it different from 着る?

着替えます is the polite present form of 着替える, which means “to change clothes” (taking one outfit off and putting another on). 着る simply means “to put on” or “to wear” clothes. Because the sentence is in polite style, 着替える becomes 着替えます.

There’s a comma after 前に. Is punctuation important in Japanese?

Modern Japanese often uses commas (読点) to clarify sentence structure and indicate pauses. In 学校に行く前に、私は家で着替えます, the comma separates the time clause 学校に行く前に from the main clause 私は家で着替えます, making the meaning clearer.

Why does the verb appear at the end of the sentence, and can I change the word order?

Japanese is generally a subject-object-verb language, so the verb comes last. Time and place expressions, topics, and objects precede the verb. While you can sometimes shift phrases for emphasis or style, the verb-ending pattern is standard and expected.

I noticed 着替ます is missing an え. Is that a typo?

Yes. The correct polite form is 着替えます, with the え after 替. Without it, the verb is incomplete and ungrammatical.