As we know, there is a class of adjectives that end in `〜らか`: `滑【なめ】らか`,
`明【あき】らか`, `清【きよ】らか`, `安【やす】らか`, etc.

`やわらか` (`柔らか` or `軟らか`) is also in this class of adjectives. However, it can
also be written as the イ-adjective `やわらかい`. So when and how did this adjective
pick up an い to become a separate イ-adjective?

Can this be done arbitrarily with any of the `〜らか` class adjectives? Like
`滑【なめ】らかい`, `明【あき】らかい`, `清【きよ】らかい`, `安【やす】らかい`. My gut feeling is that it
cannot, but only because those forms sound strange to me. If it cannot
arbitrarily be done, are there any other `〜らか` class adjectives that **can**
take on the extra い?
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2012-07-03T14:57:37.690
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question
etymology adjectives
How did やわらかい gain its い?
Firstly, as was noted in the comments (by Tsuyoshi Ito), that the same thing
cannot be done with other adjectives ending in `～らか`.

On the other hand, there exists a number of adjectives, which can function
both as イ-adjective and as ナ-adjective, e.g.

```

    大きい   大きな
    小さい   小さな
    真っ白い 真っ白な (etc.)
    細かい   細かな
    暖かい   暖かな
    四角い   四角な (etc.)
    柔らかい 柔らかな
    
```

(but, of course, やわらかい is the only one ending in `～らかい`). An investigation of
the differences here might deserve a separate question.

As for the difference in usage, I have talked to quite a few native speakers,
who maintain that there is no substantial difference in meaning between
`やわらかい` and `やわらかな`, which is only a handful of anecdotal evidence. On the
other hand, [here](http://www.yano.bc.ca/vansin/vansinpo095.htm) is an article
(blog post?) about the difference between `やわらかいお餅` and `やわらかなお餅`, where the
author says something along the lines, that a `やわらかなお餅` has a more gentle feel
to it (he says `「やわらかな」のほうが落ち着く感じがする`). Which, too, is at best anecdotal
evidence.

One can only guess that maybe he means that `やわらかい` is a more objective
statement about the physical properties of the `お餅` (softness), whereas
`やわらかな` suggests a subjective experience of softness, or rather gentleness.

But even if this is the case, not every Japanese person seems to perceive
these subtleties in the same way...

P.S. I noticed that I haven't answered your question, regarding the history of
the difference. I will delete my answer, if it isn't contributing anything to
the problem of answering your question.
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2012-09-02T01:50:41.257
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answer