| I | stiffen |
| you | stiffen |
| he/she/it | stiffens |
| we | stiffen |
| you | stiffen |
| they | stiffen |
| I | have stiffened |
| you | have stiffened |
| he/she/it | has stiffened |
| we | have stiffened |
| you | have stiffened |
| they | have stiffened |
| I | stiffened |
| you | stiffened |
| he/she/it | stiffened |
| we | stiffened |
| you | stiffened |
| they | stiffened |
| I | had stiffened |
| you | had stiffened |
| he/she/it | had stiffened |
| we | had stiffened |
| you | had stiffened |
| they | had stiffened |
| I | will stiffen |
| you | will stiffen |
| he/she/it | will stiffen |
| we | will stiffen |
| you | will stiffen |
| they | will stiffen |
| I | will have stiffened |
| you | will have stiffened |
| he/she/it | will have stiffened |
| we | will have stiffened |
| you | will have stiffened |
| they | will have stiffened |
| I | am stiffening |
| you | are stiffening |
| he/she/it | is stiffening |
| we | are stiffening |
| you | are stiffening |
| they | are stiffening |
| I | have been stiffening |
| you | have been stiffening |
| he/she/it | has been stiffening |
| we | have been stiffening |
| you | have been stiffening |
| they | have been stiffening |
| I | was stiffening |
| you | were stiffening |
| he/she/it | was stiffening |
| we | were stiffening |
| you | were stiffening |
| they | were stiffening |
| I | had been stiffening |
| you | had been stiffening |
| he/she/it | had been stiffening |
| we | had been stiffening |
| you | had been stiffening |
| they | had been stiffening |
| I | will be stiffening |
| you | will be stiffening |
| he/she/it | will be stiffening |
| we | will be stiffening |
| you | will be stiffening |
| they | will be stiffening |
| I | will have been stiffening |
| you | will have been stiffening |
| he/she/it | will have been stiffening |
| we | will have been stiffening |
| you | will have been stiffening |
| they | will have been stiffening |
| I | would stiffen |
| you | would stiffen |
| he/she/it | would stiffen |
| we | would stiffen |
| you | would stiffen |
| they | would stiffen |
| I | would have stiffened |
| you | would have stiffened |
| he/she/it | would have stiffened |
| we | would have stiffened |
| you | would have stiffened |
| they | would have stiffened |
| I | would be stiffening |
| you | would be stiffening |
| he/she/it | would be stiffening |
| we | would be stiffening |
| you | would be stiffening |
| they | would be stiffening |
| I | would have been stiffening |
| you | would have been stiffening |
| he/she/it | would have been stiffening |
| we | would have been stiffening |
| you | would have been stiffening |
| they | would have been stiffening |
| You | stiffen |
| we | Let's stiffen |
| You | stiffen |