In addition to ‘passive’ verbs, れる and られる (the auxiliary verbs) are used when expressing 可能（かのう） ‘possibility’.
られる will be attached to the base form of る-Verbs (the form after る has been removed).

• 明日（あした）までに届（とど）けられる？
  Can you deliver it by tomorrow? (Natural Japanese, and may express ‘potential’, ‘passivity’, ‘respect’, or ‘spontaneous occurrence’)
• 一人（ひとり）で全部（ぜんぶ）食（た）べられる？
  Can you eat all of this on your own? (Natural Japanese, and may express ‘potential’, ‘passivity’, ‘respect’, or ‘spontaneous occurrence’)

A common sight in modern Japanese is ラ抜（ぬ）き言葉（ことば） (words where the ら may be removed, and れる may be used by itself). However, this is not technically correct Japanese, and may cause confusion in cases where ら is required (with る-Verbs and くる, when られる is expressing ‘passivity’, ‘respect’, or ‘spontaneous occurrence’).

• トムはすぐに新（あたら）しい文法（ぶんぽう）を覚（おぼ）えれる。
  Tom is able to remember new grammar immediately. (Natural Japanese only when expressing ‘potential’, not ‘passivity’, ‘respect’, or ‘spontaneous occurrence’)
• 彼（かれ）はなんでも食（た）べれる。
  He can eat anything. (Natural Japanese only when expressing ‘potential’, not ‘passivity’, ‘respect’, or ‘spontaneous occurrence’)

For う-Verbs, they will behave a little differently. Instead of the final kana of the verb changing to an あ sound, and then adding れる (as would be the case with passive verbs), the final kana of the verb will change to an え sound (る will become れ, う will become え, す will become せ, etc.) before adding る.

• この歌（うた）は弾（ひ）けますか？
  Are you able to play this song?
• この池（いけ）では色々（いろいろ）な魚（さかな）が釣（つ）れます。
  You can catch many kinds of fish in this lake.

Interestingly, する verbs do not have a ‘potential’ form, and the verb できる will be used in its place.

• サリーはほとんどの漢字（かんじ）を書（か）くことができる。
  Sally is able to write most kanji.