What you can do

The beginner course said "I can read kanji" as 漢字かんじを読よむことができます, which is correct, formal, and about twice as long as what anybody actually says. Japanese has a potential form built into the verb, and it costs one vowel shift you have already learned for something else.

One vowel shift, again

For a group 1 verb, move the final kana of the dictionary form to the え row and add る. That is the same shift that produced the ば form in the conditionals lesson, with る in place of ば.

Group 2 replaces る with られる: 食たべる gives 食たべられる, 見みる gives 見みられる, 起おきる gives 起おきられる.

The irregulars split. 来くる behaves like a group 2 verb and gives 来こられる, with the reading shifting to こ as it does in the negative. する does not have a potential form at all: it is replaced by the separate verb できる, which is why できる has been in your vocabulary since the beginner course without ever being explained as a conjugation.

Every potential verb is a group 2 verb

Look at the right-hand column above. Every one of those forms ends in える or いる, and every one of them is a group 2 verb, whatever the group of the verb it came from. That is not a coincidence and it saves you a great deal of trouble.

書かける conjugates as 書かけない, 書かけた, 書かけなかった, 書かけて, 書かければ, 書かけたら. Every form you have learned in this course applies to it directly, with the group 2 rules, and the potential form itself never needs to be conjugated in any special way.

漢字かんじが読よめなかったので、辞書じしょを使つかいました kanji ga yomenakatta node, jisho o tsukaimashita I couldn't read the kanji, so I used a dictionary

One consequence catches people: a potential verb has no potential of its own. There is no 読よめられる. Another is that potential verbs describe states rather than actions, so they do not usually take the ている of an action in progress, and they sit comfortably with adverbs of degree such as 少すこし and よく.

Example. Give the potential form of 泳およぐ, 持もつ, 食たべる, する and 来くる, and then the plain negative past of the first.

泳およげる, 持もてる, 食たべられる, できる, 来こられる. The group 1 pair take the え-row shift; the group 2 verb takes られる; する is replaced by できる outright; and 来くる follows the group 2 pattern with its reading shifted to こ. Then, since 泳およげる is itself a group 2 verb, its negative past is formed by the group 2 rules: 泳およげない gives 泳およげなかった. Not 泳およがなかった, which is the plain negative past of 泳およぐ and means you did not swim rather than that you could not.

Now you. Give the potential forms of 聞きく, 借かりる and 帰かえる, and say why the last one is worth watching.

が where を is expected

The potential form takes が on the thing you are able to do, not を. This is the same pattern as 好すき and ほしい at the end of the beginner course, and for the same underlying reason: a potential sentence describes a state rather than an action, so its complement is a subject rather than an object.

日本語にほんごが話はなせます nihongo ga hanasemasu I can speak Japanese

ピアノが弾ひけますか piano ga hikemasu ka can you play the piano?

を is nonetheless heard and written constantly, and it is not an error. As with the たい form, が pulls the focus onto the thing itself and を keeps the ordinary transitive feel of the verb. The tendency is that を is commoner when the verb phrase is long or when the sentence is about the activity rather than the ability. Produce が, accept を, and do not correct a native speaker who uses either.

Two things are not optional. The particle on anything else in the sentence is unchanged, so 図書館としょかんで本ほんが借かりられます keeps its で. And で marking a means or a place never becomes が.

できる, and ことができる

できる is the potential of する, so any noun that takes する has a potential built from it with が.

車くるまの運転うんてんができます kuruma no unten ga dekimasu I can drive

ことができる, from the beginner course, still works and means the same thing. The difference is register. The potential form is what you say; ことができる is what you write in a notice or a formal document, and using it in conversation sounds stiff rather than wrong. When a sentence needs to state a permission or a facility, ことができる is the natural choice: このカードで買かい物ものをすることができます reads like a bank's terms and conditions, which is exactly where you will find it.

What happens by itself

Two verbs describe perception happening to you rather than your being able to perceive, and they are not potential forms at all.

ここから富士山ふじさんが見みえます koko kara Fujisan ga miemasu you can see Mount Fuji from here

隣となりの部屋へやから音おとが聞きこえる tonari no heya kara oto ga kikoeru there's a sound coming from the next room

見みえる means the thing is visible; 聞きこえる means the sound reaches you. Neither says anything about your ability or your opportunity, and neither involves a decision on your part. Set against them, 見みられる and 聞きける are true potentials and are about opportunity.

明日あしたなら、その映画えいがが見みられます ashita nara, sono eiga ga miraremasu if it's tomorrow, I can watch that film

The film is not spontaneously visible from where you are standing; you are free tomorrow, so you have the chance to watch it. That is the whole distinction: 見みえる is about the world, 見みられる is about you.

Example. Choose between 見みえる and 見みられる: (1) 眼鏡めがねがないと、何なにも＿. (2) チケットがあれば、コンサートが＿.

(1) 見みえません. Without glasses nothing registers on your eyes at all, which is a fact about the visual world reaching you rather than about opportunity. (2) 見みられます. A ticket gives you the chance to attend, which is exactly opportunity. A useful test: if the obstacle is physical and immediate, it is 見みえる; if the obstacle is a matter of arrangements, it is 見みられる.

Now you. Choose between 聞きこえる and 聞きける, and say why: (1) 声こえが小ちいさくて、よく＿ませんでした. (2) 来週らいしゅうのコンサートで、彼女かのじょの歌うたが＿.

ら抜ぬき, and a change in progress

Group 2 られる is doing three jobs at once. 食たべられる can mean "can eat", "is eaten" and, as the honorific lesson will show, "eats" said respectfully. That is an unusual amount of ambiguity for a common form, and the language is dealing with it.

In speech, the potential of a group 2 verb is very widely formed by dropping the ら: 食たべれる, 見みれる, 来これる. This is ら抜ぬき言葉ことば, "ra-dropped words", and it has been the standard example of language decay in Japanese newspaper columns for decades. It is also useful, because the ら-less form is unambiguously potential, and it fits the pattern: group 1 verbs form their potential with a plain え-row shift, and ら抜ぬき makes group 2 verbs do the same.

The Agency for Cultural Affairs runs an annual opinion survey on the Japanese language, and in its 2015 round it found that for 見みれる against 見みられる, slightly more respondents preferred the shorter form, the first time the ら-less variant had come out ahead for that verb. Younger speakers lead the change by a wide margin.

What to do about it as a learner is straightforward. Understand ら抜ぬき, expect to hear it constantly, and produce the full form in anything written and in any formal setting, where it is still corrected. This is not a rule of grammar so much as a fact about a change that is under way, and the honest position is that in twenty years the advice may be different.

Easy and hard

Two suffixes on the ます stem round out the topic, because "can" and "cannot" are often too blunt for what you mean.

やすい means easy to, and にくい means hard to. Both produce い adjectives, so they conjugate as adjectives do.

この本ほんは分わかりやすいです kono hon wa wakariyasui desu this book is easy to follow

この字じは読よみにくい kono ji wa yominikui this handwriting is hard to read

The difference from the potential is that these describe a property of the thing, not of you. 読よめない says you cannot read it; 読よみにくい says it is hard to read, which is a complaint about the handwriting. づらい is a near synonym of にくい with a stronger sense of discomfort to the speaker, so 言いいづらい is something awkward to say rather than something physically difficult to pronounce.

Example. A colleague's note is a scrawl, and there is one character in it you simply do not know. Say both things, and say why they are not the same sentence.

この字じは読よみにくいです for the scrawl, and この漢字かんじが読よめません for the unknown character. The first locates the problem in the handwriting and is a remark anyone could make about it; the second locates the problem in you. Said to the colleague, the first is a mild complaint and the second is an admission, which is a real difference in a workplace. Note the particles: にくい describes the thing, so the thing is the topic with は, while the potential takes が on what you cannot manage.

Now you. Say that this dictionary is easy to use, and that you could not use it yesterday because you had left it at home.

Vocabulary

Ability is what you could do. The next lesson is about what you have decided to do, and about the difference between a change you chose and one that happened to you.