よう, みたい, そう, らしい, and っぽい can all seem like much of a muchness at first. They are not all mutually exclusive—one phrase can substitute for another in certain cases. As you hear them used in conversation you’ll gradually develop a feel for the nuance each carries and begin to use them without thinking too much. For now, comparing them altogether should help you gain a better understanding.

あめようだ。
It seems it’s going to rain.

Context: You look at a weather map and see dark clouds moving in your direction (reasonably reliable). Sounds a little hard.

あめみたいだ。
It seems it’s going to rain.

Context: Same as the above but the expression is softer.

あめそうだ。
It looks like it’s going to rain.

Context: You look up at the sky and see dark clouds. Judgment based on your direct experience.

あめそうだ。
I heard it’s going to rain.

Context: According to someone with knowledge (maybe the weather forecast) it’s going to rain. This expression suggests your fairly confident that it will indeed rain.

あめらしい
I heard it’s going to rain.

Context: You’ve heard from a friend or someone else that it’s going to rain.

あめっぽい
[Meaning can be understood, but not “proper” grammar]

There’s no reason for a negative connotation here and, in any case, this phrase tends on to be used with certain verbs.

And another example with a noun.

ジョナサンは子供こどものようだ。
Jonathan is like a child.

Context: Maybe he’s getting in a bother about a small thing. Formal.

ジョナサンは子供こどもみたい
Jonathan is like a child.

Context: As above but less formal. Note that the auxiliary particle is almost always omitted in casual conversation unless used with よ, ね, or よね.

ジョナサンは子供こどもっぽい
Jonathan is childish.

Context: General personality trait.

ジョナサンは子供こどもそうだ。
Jonathan is a child apparently.

Context: You thought he might be an adult but you heard from someone that in fact he’s a child. This is just a factual.

ジョナサンは子供こどもらしい
Jonathan is a child apparently.

Context: As above, but less formal.

The following might help to make a distinction between らしい and っぽい.

大人おとならしい
Adult-like handwriting.

No connotation here; but obvious everyone wants to write in a “grown-up” fashion.

子供こどもっぽい
Childish handwriting.

Here っぽい is arguably more appropriate because the opposite is true and hence the sentence carries a slightly negative connotation.

かれ子供こどもっぽいよね。
He has childish handwriting, doesn’t he?
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