phraseology

today we'll be looking at the phrase "half-assed".

let's start be disassembling the phrase into it's constituent words, courtesy of dictionary.com
half (hf, häf)
n. pl. halves (hvz, hävz)
1. One of two equal parts that together constitute a whole.
2. One part approximately equal to the remaining part.
[Middle English, from Old English healf. See skel- in Indo-European Roots.]


half is a fractional term: in dividing something into two identical portions, each portion is considered a half.

ass (s)
n. pl. ass·es (sz)
1. Any of several hoofed mammals of the genus Equus, resembling and closely related to the horses but having a smaller build and longer ears, and including the domesticated donkey.
2. A vain, self-important, silly, or aggressively stupid person.
[Middle English asse, from Old English assa, perhaps of Celtic origin, ultimately from Latin asinus.]

ass is the general blanket term for a group of animals mainly used in agricultural times as beasts of burden.

coined in the late 20th century, 'half-assed' is usually used to connotate a lack of effort. thus if one were to guage an unsatisfactory performance that fell short of the apparent potential of the performer, one would say, "that was half-assed."

back in said agricultural times, when the ass was a beast of burden, it came to represent effort. from that came this phrase to express that a hypothetical bar of effort, or ass, was only partially filled. now why wasn't the phrase 'part-assed' instead? well, the 'half' half of the phrase was a cheeky reference to the ulterior slang meaning of ass - that being the buttocks, or the glutamus maximus. as you may well know, the buttocks are divided into halves by a muscular fissure so as not to impede the movement of individual legs.

expect to see this phrase evolve in the future to encompass zero-effort performances.
"dude, that was so assless."
"no ass whatsoever."
likewise, for the full-efforted:
"i am impressed. it was very whole-assed."
"wow, total-ass!"
"good job. you were all-assed."
or even, "that was assed!"