| Present "ascertain" | I | ascertain | |
| Present Continuous "ascertain" | I | am ascertaining | |
| Simple past "ascertain" | I | ascertained | |
| Past Continuous "ascertain" | I | was ascertaining | |
| Present perfect "ascertain" | I | have ascertained | |
| Present perfect continuous "ascertain" | I | have been ascertaining | |
| Past perfect "ascertain" | I | had ascertained | |
| Past perfect continuous "ascertain" | I | had been ascertaining | |
| Future "ascertain" | I | will ascertain | |
| Future continuous "ascertain" | I | will be ascertaining | |
| Future perfect "ascertain" | I | will have ascertained | |
| Future perfect continuous "ascertain" | I | will have been ascertaining |