seem, do not/ are bot

If you say "do not", it means that the third and fourth do not seem contradictory.

If you say "are not", it means that the third and fourth are not contradictory (according to you, at least).

I would say "first and second notions".

HifaMoPlease which of the following is correct?
The first and second notions may seem contradictory, but the third and fourth do not/are not.

Both are possible. The choice depends on whether you want to say that they don’t seem contradictory or that they aren’t contradictory.

edit: coss-posted with GPY

GPYI would say "first and second notions".

Since you said 'I would say,' is it just a personal preference?

Thank you

Only the plural works for me.

I still didn't get it.

Do you mean for others it may be correct, but for you it is not?

In other words, are there variations in this use?

Thank you.

HifaMoDo you mean for others it may be correct

I didn’t think so when I answered, hence the ‘correction’ I made, but now I’m not sure.

I wondered whether "the first and second notion" could be understood as an ellipted version of "the first notion and the second notion". I can't seem to decide whether this is viable or not.

Thank you.
I hope to see other members' views.

GPYI wondered whether "the first and second notion" could be understood as an ellipted version of "the first notion and the second notion".

That would be my interpretation, but it still sounds wrong to me.

GPYI wondered whether "the first and second notion" could be understood as an ellipted version of "the first notion and the second notion". I can't seem to decide whether this is viable or not.

I would use only the plural notions, but I hesitate to say the singular is wrong.