ごとき / ごとく / ごとし / 如き / 如く / 如し【ごとき / ごとく / ごとし / ごとき / ごとく / ごとし】

ごとく, ごとき and ごとし mean "like", "as if". They are three forms of one literary word and do the work of modern ように, ような and ようだ: ごとく describes a verb or an adjective, ごとき describes a noun, ごとし ends the sentence. A noun takes の before them. In kanji they are ごとく如く, ごとき如き and ごとし如し, and both spellings are common.

The forms are not interchangeable. Before a noun it has to be ごとき: ×夢のごとく日々.

After a verb

A verb takes が between it and ごとく – an old use of が that works like の. With かの in place of が, the comparison is counterfactual: "as if", when it isn't so.

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All three belong to writing, speeches, proverbs and set phrases. In conversation the same sentence uses ように, ような or みたい, and ごとく would sound theatrical.

ごとき for belittling

Straight after a noun, without の, ごとき means "the likes of", "a mere". Said of someone else it is contempt; said of yourself it is humility.