The other day I was musing on chat about 忘れれれば, which I imagined you would get if you started with 忘れられれば and left out ら:
- 忘れられる （忘れる ＋ られる）
- 忘れられれば （忘れる ＋ られる ＋ れば）
- 忘れれれば （忘れる ＋ られる ＋ れば ー ら）
Of course, it sounds a little silly, but I thought it might be a possible example of the so-called ら抜き言葉, where ら is left out of a verb form with 〜られる.
I've read about ら抜き言葉 before, but I'm afraid I've forgotten where! And I'm having trouble finding the reference again. I do have Martin 1975, but it's been almost 40 years since it was written, so I think it's likely to be out of date on this point.
If I recall correctly, I read about some tendencies like "it occurs more often with negatives" and "it occurs most often with short verbs". So I'm aware that it's not really as simple as dropping ら from any form with 〜られる, but I'm not quite sure what the rules are.
I guessed that a form like 忘れれれば would be uncommon. But when I asked about it on chat, 非回答者さん helpfully responded:
[...] no one says 忘れれれば. It is not a matter of how often it is said. That form does not exist in the first place.
If it doesn't exist, there must be a reason ら抜き doesn't occur. What is this reason? Is it because the verb is too long? Or is there perhaps a rule against using ら抜き with verbs ending in 〜れる? Or is it something else?