What's the difference between 伸ばす and 伸べる?

Question

Just for example, can I say both 手を伸ばす and 手を伸べる? Is there any difference between them? Are they interchangeable?

If it's possible, make similar examples, please.

Answer 1

手を伸べる (or 手を差し伸べる) is a set phrase that means "to offer/extend a helping hand". I confirmed 47 out of the 50 examples of 伸べ in BCCWJ are used as part of this set phrase. Although dictionaries explain several other historical usages of 伸べる, you have almost no reason to use 伸べる outside this set phrase in modern standard Japanese. (Not to be confused with 述べる, which is very common. 延べる is uncommon but usable in modern Japanese.)

伸ばす is a very common verb that means "to extend/elongate/lengthen". 手を伸ばす can mean several things:

1. to (physically) extend one's arm (to pick an object); to (physically) reach for

   棚に手を伸ばして本を取り出した。

2. to extend an (often evil) hand (to dominate/harm)

   ローマ帝国は周囲の国に次々と手を伸ばし、領土を拡大していった。

3. to diversify and try (something new)

   彼は貯金だけで満足できず、株式投資にも手を伸ばし始めた。