When is it proper to use "more rare" rather than "rarer"?

Welcome to the Agora, metanoia.

The general rule for forming comparative adjectives is that if the root has one or two syllables, it can take either the -er suffix or the "more" construction, although the suffix is more common in everyday usage. Adjectives with three or more syllables only take the "more" construction.

So you’d say "sweeter" but not "beautifuler"; "bigger" but not "interestinger".

Like most rules in English, there are exceptions. "Rarer" is by no means incorrect but it’s a bit of a mouthful because there are no plosives or fricatives in the phonology, so some people might favor the "more rare" form.

- PW

Thanks Palewriter. That was a very clear and interesting reply. I am already happy I found this site and forum. Have a good day!

Bravo, PW!  Good answer!  An answer most rare (or is it ‘rarest’?)!

Sitran

Well thank you, Sitran. Possibly to celebrate my first serious Agora post in weeks, I took my wife out to an eminent restaurant this evening. We each devoured a delicious tenderloin steak. Mine was somewhat rarer than hers. Still dizzy from the steak experience, I suppose, we ordered an apple pie a la mode with flaming brandy butter sauce for desert. It was a dining experience that couldn’t have been more rare.

- PW
who watches his calories; there are lots of them

The most rare, indeed, you are!

‘Twas ‘bout time ya took’r out.  Sounds like a great time!

Not so rare, I hope!

Sitran

Well, Metanoia, as Palewriter said, both "rarer" and "more rare" are fine.  As for style ... Shakespeare used both:

Sonnet 56, line 14

Make summer’s welcome, thrice more wished, more rare.

The Tempest Act 5 scene 1 line 31/2:
                The rarer the action is
In nature than in vengeance.

Macbeth, Act 5, scene 8:

We’ll have thee, as our rarer monsters are
Painted on a pole, and under write
‘Here may you see the tyrant.’

So I guess we’re free to choose which ever fits the situation.

bnjtokyo

Hehehe, his conversation turned up in a Fabebook argument, it was a delight to find it, but then I realised that I possibly made an ass of myself (that’s the animal, not the body part) and deleted everything I said before.