不是...就是 presents two alternatives where one must be true. It can express:
Two possibilities - If not A, then definitely B
Habitual alternatives - He is always either doing X or Y
Limited options - Only two choices exist
He is either reading, or sleeping.
Often used to describe habits or to narrow down possibilities.
Different from 要么...要么 (which you have)
- 不是...就是 implies certainty (one MUST be true)
- 要么...要么 presents choices without certainty
Can describe habitual behavior
- Often with slight complaint or observation tone
Word order is fixed
- Cannot swap the two options
He is either reading, or sleeping.
This is either your fault, or his fault.
On weekends I either go to the gym, or go jogging in the park.
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