前者は / 後者は【ぜんしゃは～こうしゃは】

前者は (the former) and 後者は (the latter) are used to refer back to two items, people, or ideas that have already been mentioned, distinguishing between the first and the second. They function similarly to "the former" and "the latter" in English and are used in written language, formal speech, essays, and explanations.

These words are used when comparing or contrasting two things that were introduced in the previous sentence or clause. They help avoid repetition and make writing more concise.

You do not always need to use both together – it is possible to use just ぜんしゃ前者 or just こうしゃ後者 when you only need to highlight one of the two.

Notes

• 前者は and 後者は are primarily used in written and formal contexts. In casual conversation, speakers usually just repeat the nouns or use demonstratives like こっち and あっち.
• The particle after ぜんしゃ前者 / こうしゃ後者 changes depending on the grammatical role (e.g. 前者が、前者を、前者の), but the は-marked topic form is the most common pattern.
• These terms strictly refer to two items. For three or more, other expressions are used.