Rashii, Rashiku, and Rashisa

Question

I know Rashii（らしい） is an i-adjective. What are the forms Rashiku（らしく） and Rashisa（らしさ） that I see often used?

Answer 1

Background: Conjugation

The word らしい conjugates the same as any other -i adjective. Here are the basic forms, with their names in Japanese and English:

• Ending in い
  終止形【しゅうしけい】 terminal / predicative (used to end a sentence) and 連体形【れんたいけい】 attributive (used to modify a noun or noun phrase)
• Ending in く
  連用形【れんようけい】 adverbial (used to modify another verb or adjective, sometimes used as a conjunctive to say "this and [whatever comes next]")
• Ending in くて
  接続【せつぞく】 conjunctive (formed from the adverbial + て, used to say "this and [whatever comes next]")
• Ending in さ
  名詞【めいし】 noun or nominal (similar to "-ness", used to describe the objective degree or "how much" of an adjective)
• Ending in み
  名詞【めいし】 noun or nominal (similar to "-ness", used to describe the subjective impression or feeling of the adjective)

Your Questions

• What is らしく?

らしく is the adverbial form of らしい. While a phrase like 「XYZらしい」 means that something is "like XYZ", or "seems XYZ-ish", a phrase like 「XYZらしく」 would mean "in an XYZ manner" as an adverbial, or "seems XYZ-ish, and [whatever comes next]" as a conjunctive.

• What is らしさ?

らしさ is the noun form of らしい. While a phrase like 「XYZらしい」 means that something is "like XYZ", or "seems XYZ-ish", a phrase like 「XYZらしさ」 would mean "XYZ-ish-ness", in terms of the degree or "much-ness" of the XYZ-ish quality.