彼は確かに頭が切れる。

he; him; his; boyfriend

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

sure; certain; positive; definite; reliable; trustworthy; safe; sound; firm; accurate; correct; exact; If I'm not mistaken; If I remember correctly; If I remember rightly

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

head; hair (on one's head); mind; brains; intellect; leader; chief; boss; captain; top; tip; beginning; start; head; person; top structural component of a kanji

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

to break; to snap; to be cut; to split; to crack; to be injured; to wear out; to be worn out; to break; to burst; to collapse; to wear off; to stop working; to go dead; to expire (time limit, etc.); to run out; to become due; to run out (of stock, etc.); to be exhausted; to be used up; to be sold out; to be out of; to be broken off (e.g. of a relationship); to break up; to have severed ties; to be cut off; to be disconnected; to cut well; to be sharp; to be sharp-minded; to be keen; to be shrewd; to be quick-witted; to be able; to be short of; to drop under (a certain figure); to beat (e.g. a record time); to dry off; to curve; to veer; to shuffle (cards); to get angry; to snap; to blow one's top; to lose one's temper; to flip; to be able to do completely