Present
| I | stiffen |
| You | stiffen |
| She | stiffens |
| We | stiffen |
| They | stiffen |
Past
| I | stiffened |
| You | stiffened |
| She | stiffened |
| We | stiffened |
| They | stiffened |
Perfect
| I | have | stiffened |
| You | have | stiffened |
| She | has | stiffened |
| We | have | stiffened |
| They | have | stiffened |
Future
| I | will | stiffen |
| You | will | stiffen |
| She | will | stiffen |
| We | will | stiffen |
| They | will | stiffen |
Past Perfect
| I | had | stiffened |
| You | had | stiffened |
| She | had | stiffened |
| We | had | stiffened |
| They | had | stiffened |
Future Perfect
| I | will | have | stiffened |
| You | will | have | stiffened |
| She | will | have | stiffened |
| We | will | have | stiffened |
| They | will | have | stiffened |
Present - Conditional
| I | would | stiffen |
| You | would | stiffen |
| She | would | stiffen |
| We | would | stiffen |
| They | would | stiffen |
Perfect - Conditional
| I | would | have | stiffened |
| You | would | have | stiffened |
| She | would | have | stiffened |
| We | would | have | stiffened |
| They | would | have | stiffened |