Coming from the こそあど言葉(ことば) family of words, こう, そう, ああ, or どう may be used with the verb 言(い)う to form an expression which literally means 'in the way of (A)'. (A) being 'this' これ, 'that' それ, 'that over there' あれ, or 'what' どれ (in questions). As with all pre-noun adjectival words, this expression will be used directly before a noun.

Although こう, そう, ああ, and どう share a relationship with これ, それ, あれ, and どれ, they are their own individual words, which each have a meaning similar to 'as such'. These words are all adverbs when used by themselves.

Caution

そう (the adverb), should not be confused with そう, the auxiliary verb. そう (the adverb) comes from the kanji 然(そ)う, while the auxiliary verb does not have a kanji form.

よう (and う) are grammar constructions that function in a similar way to ましょう, or to be more precise, ましょう is the polite (conjugated) form of these auxiliary verbs. They are used as a casual way of expressing 'let's' when making suggestions, or 'I shall' when making statements.

よう is only one of the potential forms of this grammar point, and can actually be divided into two separate auxiliary verbs, う (used with う-Verbs), and よう (used with る-Verbs, する, and くる).

When attaching う to う-Verbs, simply replace the last kana with the equivalent お sound kana from within the same column (く becomes こ, う becomes お, す becomes そ, etc.), before adding う. For る-Verbs, replace る with よう.

As with many other verb conjugations, する and くる behave in a slightly different way to regular う-Verbs and る-Verbs. する will become しよう, while くる will become こよう.

The type of statements that う, and よう can be used for in Japanese are usually divided into three categories.

推量(すいりょう) - Expresses guesses (has a similar meaning to だろう, which itself is the よう form of だ)

意志(いし) - Expresses intentions (has a similar meaning to ～するつもりだ)

勧誘(かんゆう) - Expresses invitations or encouragement (has a similar meaning to 誘(さそ)う 'to invite')

Caution

Although よう is used with る-Verbs, する, and くる, it should not be confused with ようだ, another auxiliary verb that is used when describing likeness (in a similar way to そうだ).

In a similar way to みたい, ようだ is used when making observations about something in Japanese. This auxiliary verb is used to express three primary things.

たとえ - Using (A) as an example to highlight the way that (B) looks/is acting.

推定(すいてい) - Using (A) as a reason for an assumption made about (B).

例示(れいじ) - Presenting (A) as an example of what (B) is.

ようだ is usually based on direct information/experience, and shows that the speaker has high confidence in what they are saying. It may also frequently appear in its kanji form, 様(よう)だ.

ようだ can be used with any verb, い-Adjective, な-Adjective, or noun. However, it requires な before it when used with な-Adjectives, or の when used with nouns.

Although ようだ and そうだ are often used in similar situations, そうだ shows that the speaker has a lot less confidence in their statement than ようだ. Because of this, ようだ is a much better choice when stating things that are obvious/observable by anyone.

Caution

ようだ is considerably more formal than みたい, and is therefore less common in casual conversation.