The English word "How" can be translated into several different words in Japanese. So I think it is probably best if we first take a look at some example phrases with "How" in Japanese.
Basically, the English word "How" in Japanese is "どう."
The word "いかが" is a politer word for "how" in Japanese. You can actually say "ご機嫌どうですか？" But the preceding word "ご機嫌" is a polite word to mean "mood" or "feeling." So "いかが" goes better with "ご機嫌" than "どう" If you want to use "どう" to say "How are you?" you can say "調子(ちょうし)はどうですか？" which is a little less polite.
If you are asking "by what means," in Japanese we use『どうやって』like the example No. 4 above.
If you are asking "by what manner," in Japanese we use 『どのように』like the example No. 5 above. ※But the difference between 『どうやって』and 『どのように』are very subtle.
You can't say『いかがやって』.
『いかが』is a politer word for "how," but you can't say 『いかがやって』instead of 『どうやって』. We just simply can't.
Please create your own sentences using 『どう』『いかが』『どうやって』and 『どのように』. Write at least two example sentences for each. We will check your answers during the next lesson.
日本最大級のebookサイト紹介：Good for brushing up your Japanese!
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