Difference between 〜っぽい, 〜がち, and 〜やすい?


From what I understand, 〜っぽい, 〜がち, and 〜やすい all seem to suggest that someone
has a general tendency towards doing something. It seems that 〜っぽい and 〜がち can
attach to a noun or to the 連用形 of a verb, while 〜やすい can attach to the 連用形 of
a verb.

All three can be used in a sentence such as:

  * 彼女は大事なことを忘れっぽい。
  * 彼女は大事なことを忘れがちだ。
  * 彼女は大事なことを忘れやすい。

Is there a difference in meaning between these phrases?




All three of the phrases are similar in that they are about conveying how
something, or someone, _appears to you_. However, they do have different
meanings that change the nature of what that appearance is.

  * 彼女は大事なことを忘れっぽい。

"She **_seems like_** the type who forgets important things." This is
emphasizing how she appears to you, so it may or may not be the case that she
does in fact forget important things, but it seems that way to you. You might
want to compare and contrast [`~っぽい`, `~みたい`, and
`~らしい`](https://japanese.stackexchange.com/a/2401/119).

  * 彼女は大事なことを忘れがちだ。

"She **_tends to_** forget important things." In this case you are more
certain of your personal assessment, but within that assessment you are saying
that while she usually forgets important things, you also allow that she
doesn't always.

  * 彼女は大事なことを忘れやすい。

This would be "she forgets important things **_easily_**." Where `~がち` is
about how often she forgets, `~やすい` is about how reliably she forgets.
However, as mentioned in the comments, I'm not sure `~やすい` can be applied to
people. Someone can correct me on this, but I think it would be more
grammatical to say something like `彼女にとって、大事なことが忘れやすい`, which would be "For
her, important things are easy to forget."




All three of the phrases are similar in that they are about conveying how
something, or someone, _appears to you_. However, they do have different
meanings that change the nature of what that appearance is.

  * 彼女は大事なことを忘れっぽい。

"She **_seems like_** the type who forgets important things." This is
emphasizing how she appears to you, so it may or may not be the case that she
does in fact forget important things, but it seems that way to you. You might
want to compare and contrast [`~っぽい`, `~みたい`, and
`~らしい`](https://japanese.stackexchange.com/a/2401/119).

  * 彼女は大事なことを忘れがちだ。

"She **_tends to_** forget important things." In this case you are more
certain of your personal assessment, but within that assessment you are saying
that while she usually forgets important things, you also allow that she
doesn't always.

  * 彼女は大事なことを忘れやすい。

This would be "she forgets important things **_easily_**." Where `~がち` is
about how often she forgets, `~やすい` is about how reliably she forgets.
However, as mentioned in the comments, I'm not sure `~やすい` can be applied to
people. Someone can correct me on this, but I think it would be more
grammatical to say something like `彼女にとって、大事なことが忘れやすい`, which would be "For
her, important things are easy to forget."

