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I've long known 冷やす as the transitive counterpart of 冷える. But thanks to one question here, I've realized that there is another version with an extra syllable in it: 冷やかす. Although 冷やかす seems to have secondary meaning of making fun of someone, the first meaning "to refrigerate" seems to overlap with 冷やす. Is there any difference between them?

Being curious, I looked up in the dictionary for other verbs that have "Xsu" and "Xkasu" variants and found another pair: 散らかす and 散らす. Same question, how are they different?

Lastly, are there any other verb pairs that are different in look from each other by one additional syllable while still maintaining transitivity, and would there be any pattern on how the verbs in each pair different from each other?

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up vote 6 down vote accepted

In case of 散らす and 散らかす, 散らす is purposefully done while 散らかす is kind of a by-product that happened while you were trying to do something else.

金箔を散らす -> Decorate by sprinkling it with gold flakes.
金箔を散らかす -> While decorating, litter the gold flakes (and not clean up afterwards)

冷やかす is a bit archaic (don't ask me why!) so I'll use 寝かす instead to illustrate the point. Here, かす means "to force something to do something". For example, 子供を寝かせる means "Make the child sleep". In case of 冷やかす, it means to "Make something chill" (literal meaning: "let something chill itself").

I guess this makes some sense in regard to 散らす/散らかす distinction, because the literal meaning of 散らかす is "Let something litter itself". Basically the person is allowing (negligently) the gold flakes to scatter around, while in case of 散らす, the person is actively scattering the gold flakes (by himself).

Another example is やらかす which is a slang for "screw up". I'm not sure what the etymology for this is though.

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Does 聞かす have the same nuance? Also, does this かす with meaning "to force something to do something" the reason why many intransitive verbs ending with く have transitive counterparts that end with かす? -> 動く/動かす, 驚く/驚かす etc (cf. 届く/届ける). – Lukman Sep 22 '11 at 7:19
According to 大辞泉: かす (接尾) 動詞の未然形について動詞をつくり、そのようにさせるという意を表す。 Following that, the other verbs you cite would end up as 動かかす and 驚かかす, although I would suppose it's possible that one of the か's got dropped somewhere along the way. – rdb Sep 22 '11 at 20:27
@Lukman: Yep, 聞かす has the same nuance. E.g. 音楽を聞かす (have he/she listen to music). Not sure about your 2nd question. – Enno Shioji Sep 23 '11 at 1:43

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