This verb follows the standard English past tense rule: simply add -ed to the base form.
Co-sign is regular. It follows the Standard -ed rule.
Use past time markers: "Yesterday, she co-signed to the store."
No. Use "did not co-sign" (not "did not co-signed").
The verb co-sign follows the standard English past tense conjugation rule. When forming the past tense, co-sign becomes co-signed. This follows the Standard -ed pattern, which is one of the most common conjugation rules in English.
Understanding why co-sign becomes co-signed helps with spelling and pronunciation. This verb follows the standard English past tense rule: simply add -ed to the base form.
When using co-signed in writing, remember that it functions as a past tense verb and typically appears with time markers like yesterday, last week, or ago. For example: "Yesterday, she co-signed to the store." The past tense form does not change based on the subject — I co-signed, you co-signed, he/she co-signed, we co-signed, they co-signed.