A potty mouth is a force multiplier

病は口より入り禍は口より出ず
(Yamai wa kuchi yori iri wazawai wa kuchi yori izu;
“Disease enters from the mouth and disaster exits from the mouth”)

Definition:

Disease enters the body through your mouth when you eat and drink; calamity and misfortune arise from the words that come out of your mouth. A warning to be careful with one’s words.

Breakdown:

This is another saying composed of two parallel phrases; in this case verb phrases. In the first we have the noun 病 (yamai), “sickness,” marked as the topic of discussion by the particle は (wa). This is followed by the noun 口 (kuchi), “mouth,” marked as the origin of some motion by the particle より (yori), “from.” The motion in this case is 入る (iru), “to enter,” in conjunctive form. (Note that, just as in last week’s saying, this is an archaic form of the verb.)

The second half has in place of sickness 禍 (wazawai), “calamity,” and the repetition of は creates an explicit contrast between the two halves of the saying, beyond the effect of the parallel structure. 口より is as before, but in this case the verb is 出ず (izu), an archaic form of the verb now mostly seen as 出る (deru), “to go out,” although izu is more commonly found as 出づ. Izu appears here in sentence-final form.

Notes:

Obviously this saying displays an incomplete understanding of disease. But given the antiquity of its origins and focus on the need for cautious speech, I’m sure that can be forgiven. The kotowaza apparently comes to us from third-century Chinese poet Fu Xuan (傅玄) via the Man’yoshu.

This saying may be invoked in abbreviated form as 禍は口から. It can also be thought of as a more egalitarian variation on the same theme as 綸言汗の如し. Closer to home, there are a number of other phrases associating catastrophe with (thoughtless words that come out of) one’s mouth, such as 口は禍の門 (kuchi wa wazawai no kado, “The mouth is disaster’s gateway”).

Example sentence:

「病は口より入り禍は口より出ずというので、毎日ジャンクフードを食って、常に気まぐれにツイートを放っている彼奴は、きっといつも色んな禍を招いてるに違いない」

(“Yamai wa kuchi yori iri wazawai wa kuchi yori izu to iu no de, mainichi jankufuudo wo kutte, tsune ni kimagure ni tsuiito wo hanatteiru aitsu wa, kitto itsumo ironnna wazawai wo maneiteru ni chigai nai.”)

[“They say that disease comes in through the mouth and disaster comes out of it, so that guy eating junk food every day and tweeting on a whim is doubtless inviting all kinds of disasters.”]