Okay so i was watching the video where JY tells us how to distinguish between Valid and Invalid argument forms and at the end he gave us a little trick to remember how to distinguish between the two and that was that:

In the valid forms, the existential statements appear first and then the universal statements.

So an example is

A some-> B-> C

-------------------

A some ->C

And in the invalid forms the universal statements appear first and then the existential statements.

So an example of this would be:

A --> B some-> C

---------------------------

A some->C

BUT, the problem is that this doesnt hold true for VALID forms 6-8 as they start with universal statements rather than existential statements. So can someone tell me a trick to remember those three.

Thanks!