Third Declension I-Stem

I received this comment:

I am currently in my first year of Visual Latin.

I’m confused… how do you tell if a 3rd declension neuter noun is i-stem or not?

Gratias ago.

Here is my reply:

This is a tricky issue.  These extra videos may help:

Third declension: https://www.youtube.com/watch?v=XlRhvU1ak1k

Third declension i-stem: https://www.youtube.com/watch?v=aDVCLySMvU8

Third declension neuter: https://www.youtube.com/watch?v=uqfw_WtKTQw

Let me know if you need any more help.