Historical/Linguistic explanation for the conditional in (seemingly) non-conditional situations?

Question

In Japanese there are conditional sentences that translate well into the English conditional:

1. お金があればいいね。
   It would be nice if I had money.

2. 食べなければ病気になるよ。
   If you don't eat you'll get sick.

These sentences line up well with the "If A, then B" pattern in English.

However, there are also a few grammar patterns in Japanese that use the conditional that don't translate well into English:

3. 考えれば考えるほどわからなくなる。
   The more I think about it, the less I understand.

4. 本を読むのが好きな人もいれば、嫌いな人もいます。
   There are those who like reading books and those who do not.

5. 彼女は国語も上手なら、数学も上手だ。
   Not only is she good at Japanese, she's also good at math.

Is there a historical or linguistic reason why these (seemingly) logically different uses of the conditional tense exist? Is the problem a lack of imagination on my part? Is it inherently wrong to compare ば/なら as if they were 1:1 equivalents to the English conditional?

Thanks in advanced for your input.

Answer 1

You may need to expand the concept of "conditional" a little bit and think of ば as a marker for "triggers" in general. ば is not only for "If A then B", but also for "A and then B", "When A, B", "Whenever A, B", or even "Since A, B". In medieval times, it even gained a meaning of "A whereas/while B".

• 気がつけば既に夜が来ていた。
  When I realized it, night had already fallen.
• ここまで来れば安全です。
  Since we've come this far, we're safe.
• ボタンを押せばいつでも水が出ます。
  Whenever you press the button, water comes out.
• 好きな人もいれば嫌いな人もいる。
  Whenever/While/Whereas there are those who like it, there are also those who dislike it.

In classical Japanese, ば meant both "if" and "since/when/whenever" depending on the conjugation of the preceding verb. For example, 書かば meant "If I write", but 書けば meant "Since I (will) write"! See this and this for details. The form like 書け (to which ば would be attached) is called "hypothetical form" (仮定形) in modern Japanese, but the same form was called "realis form" (已然形; literally "already-so form") in classical Japanese. (This form without suffixes like ば is not an independent, distinct word form in modern Japanese, but it was in classical Japanese.)

This is why, even in modern Japanese, ば sometimes feels closer in meaning to "since" or "whenever" than to "if". In modern Japanese, 書かば and 書けば have merged into one (書けば), and we use it mainly for truly hypothetical expressions, hence the name 仮定形. But we still see exceptional cases, and that's understandable because ば has never been just for "true if".

By the way, in Japanese grammar, the if-type connection is called 仮定条件 ("hypothetical conditional"), and the since-type connection is called 確定条件 ("realized(?) conditional"). 確定条件 is probably not what you imagine when you hear "conditional", but they are considered two kinds of conditional.