Verbs ending in a consonant followed by -y change the -y to -ied in the past tense form.
Theory is regular. It follows the -ied Conversion rule.
Use past time markers: "Yesterday, she theoried to the store."
No. Use "did not theory" (not "did not theoried").
The verb theory follows the standard English past tense conjugation rule. When forming the past tense, theory becomes theoried. This follows the -ied Conversion pattern, which is one of the most common conjugation rules in English.
Understanding why theory becomes theoried helps with spelling and pronunciation. Verbs ending in a consonant followed by -y change the -y to -ied in the past tense form.
When using theoried 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 theoried to the store." The past tense form does not change based on the subject — I theoried, you theoried, he/she theoried, we theoried, they theoried.