To understand the role of sound in the formation of the kanji, we have to look back to ancient China, where the script originated.

When the speakers of Old Chinese had to write down a word for which no character had been invented yet, they turned to one strategy time and time again:

1. Find a character that has a vaguely related meaning.
2. Find a character for a word that sounds alike.
3. Squish the two characters together!

Case study: the character 星 star

For instance, take the Old Chinese word for "star", which sounded something like sleng. Following that process, some ancient Chinese folks created the character for star more or less like so:

1. Find a character that has a vaguely related meaning.
   Stars appear in the sky, like the sun. So we'll take the character 日 sun.
2. Find a character for a word that sounds alike.
   Sleng sounds just like the Old Chinese word for live, so we'll take the character 生 live.
3. Squish the two characters together!
   日 sun + 生 sleng = 星 star!

When a kanji component has been used for its sound value, like 生 here, it's known as an 音符 onpu in Japanese, meaning something like "sound indicator". Since they are a subset of the kanji components, I refer to them here as sound components.

Something like half of all Japanese words have Chinese roots. In addition to being written in kanji, these words are pronounced using Japanese approximations of ancient Chinese sounds. These Sino-Japanese pronunciations of the kanji are called 音読み on'yomi, meaning sound readings.

An awareness of the kanji's sound components will go a long way towards helping you pronounce words read using on'yomi. Once in a while, you might even be able to guess the pronunciation of words containg kanji or readings that you've never encountered before.

For example, if you know any of the following words:

• 先生 sensei (teacher)
• 学生 gakusei (student)
• 生活 seikatsu (life)

...then you know that the kanji 生 live has the on'yomi セイ sei.

With the knowledge that 生 can serve as a sound component, you have an immediate advantage when learning words like the following:

• 火星 kasei (Mars)
• 姓名 seimei (first and last name)
• 性格 seikaku (personality)

As you can see, even though the characters' readings don't have much to do with the original Chinese pronunciations anymore, the sound components still provide us with some useful information as students of Japanese. Kanji that sounded similar in premodern China still tend sound similar in modern Sino-Japanese words.

To be clear, it's not always as easy as in the examples above! Some sound components only vaguely hint at a character's sound, via rhyme or looser connections, obscured by the passage of time. Moreover, the fact that a component can serve as a sound mark doesn't mean that it always does. For example, 産 give birth is pronounced not as セイ sei, but サン san.

But even the absence of a sound component can tell you something about a kanji. To illustrate, let's take that same example 産, where the component 生 fails us as a sound indicator.

When we learn that 産 give birth is read as サン san, we know right away that 生 live is not a sound component. And since it's not being used for its sound, we can deduce that it's most likely being used for its meaning instead. Indeed, the meanings of 生 live and 産 give birth are closely related: birth is the start of life. Components used in this way are called meaning components (in Japanese 意符 ifu). They provide you with a focal point for remembering the meaning of the character.

Sound components and meaning components go hand in hand; awareness of one enhances your awareness of the other. Together, they reveal the logic behind the structure of the kanji. Kanjisense helps you stay attuned to the presence of sound components by clearly indicating them prominently in multiple places. In this way, you can not only remember the kanji's pronunciation better, but you can also gain insight into its structure and meaning.

There are also native Japanese readings, the 訓読み kun'yomi, meaning expository readings, and these are just as important as on'yomi. Some kanji are used primarily for their kun'yomi, with their on'yomi seldom appearing in modern Japanese. A few kanji, being native Japanese inventions (国字 kokuji), don't even have an on'yomi.

But the name 音読み on'yomi (sound reading) hints that the Chinese-derived pronunciations somehow embody the kanji's essential sound. Accordingly, in Kanjisense, the kun'yomi take a backseat to the on'yomi and English keywords. The kun'yomi are treated in character entries, but the Kanjisense UI prioritizes the on'yomi throughout.

Now, a kanji doesn't really have one essential sound. But learners will benefit from treating the on'yomi this way during kanji study. Paying special attention to the on'yomi has some practical advantages. The first has already been mentioned above: an understanding of on'yomi and sound indicators helps you identify meaning indicators. This is key to understanding the logic behind a character's structure. Another benefit applies when you're quizzing yourself on a kanji's meaning.

If you've gotten beyond the very beginning stages of your studies, you've likely come across the problem of kanji with similar meanings. Say you're studying with flashcards, and you come to a flashcard with the English keyword use on the front. You definitely know the kanji 使 use, but you slip up and give the answer 用 utilize instead--now what? If you're using paper flashcards, do you put the card back in the pile? If you're using something like Anki, do you mark this card as a failure, and lose your progress, even if you're sure you know that kanji?

This is a minor problem in the grand scheme of things, and if it hasn't bothered you in your studies, you don't have to worry about it, at least for now. But in case this is something that has bothered you in the past, you can remedy the situation by including the on'yomi when you're testing your recall of kanji meanings.

The chance for confusion is much smaller when you quiz yourself with cards looking like:

• シ
  utilize
• ヨウ
  use

Just for the sake of thoroughness, here's another example of two kanji with similar meanings, who also share a component: 欄 and 柱. Normally, the similarity in shape and meaning could easily throw you off.

• チュウ
  pillar
• ラン
  column

If you know your sound components 闌 and 主, it's nearly impossible to mix up the two.

If you're worried that this makes things too easy, remember that when you get to the point where you're actually writing out or typing a Japanese word in real life, you will likely have both the pronunciation and meaning in your mind before you think of the kanji. In this way, a kanji-recall quiz starting from the kanji's meaning and reading might actually be a better test of your skills than a kanji-recall quiz from meaning alone.

Now, Kanjisense is still in its early stages, so many of the on'yomi prominently displayed throughout may be rare or even obsolete in modern Japanese. However, even nonsense syllables have their place in education--ask any musician who has studied solfege. You could do worse than to keep a few extra on'yomi in your head.