| Simple | Progressive | Perfect | Progressive |
| Present |
| I stiffen |
| you stiffen |
| he/she/it stiffens |
| we stiffen |
| you all stiffen |
| they stiffen |
|
| I am stiffening |
| you are stiffening |
| he/she/it is stiffening |
| we are stiffening |
| you all are stiffening |
| they are stiffening |
|
| I have stiffened |
| you have stiffened |
| he/she/it has stiffened |
| we have stiffened |
| you all have stiffened |
| they have stiffened |
|
| I have been stiffening |
| you have been stiffening |
| he/she/it has been stiffening |
| we have been stiffening |
| you all have been stiffening |
| they have been stiffening |
|
| Past |
| I stiffened |
| you stiffened |
| he/she/it stiffened |
| we stiffened |
| you all stiffened |
| they stiffened |
|
| I was stiffening |
| you were stiffening |
| he/she/it was stiffening |
| we were stiffening |
| you all were stiffening |
| they were stiffening |
|
| I had stiffened |
| you had stiffened |
| he/she/it had stiffened |
| we had stiffened |
| you all had stiffened |
| they had stiffened |
|
| I had been stiffening |
| you had been stiffening |
| he/she/it had been stiffening |
| we had been stiffening |
| you all had been stiffening |
| they had been stiffening |
|
| Future |
| I will stiffen |
| you will stiffen |
| he/she/it will stiffen |
| we will stiffen |
| you all will stiffen |
| they will stiffen |
|
| I will be stiffening |
| you will be stiffening |
| he/she/it will be stiffening |
| we are stiffening |
| you all will be stiffening |
| they will be stiffening |
|
| I will have stiffened |
| you will have stiffened |
| he/she/it will have stiffened |
| we will have stiffened |
| you all will have stiffened |
| they will have stiffened |
|
| I will have been stiffening |
| you will have been stiffening |
| he/she/it will have been stiffening |
| we will have been stiffening |
| you all will have been stiffening |
| they will have been stiffening |
|
