Why is there a negation of "ability" but not a negation of "agility"?

Question

Would like to know what is the reasoning behind the use of some prefixes for example if one were to use "un-"able as opposed to "dis-"able the situational context is understood yet the same does not apply for agile.

In software development the Agile methodology is a cultural mindset adopted by organizations to respond to change in a responsive manner. In the 90s to the early 00s there was a great amount of frustrations experienced in the software industry. Software and products were frequently delivery over budget, late and of poor quality. Traditional project management is defined in the control of cost, scope and schedule which is the opposite of dealing with high rates of change or chaos that is typically found in software development. Agile practices were created to mitigate these risks and develop ways to empower software developers to deliver high quality products at cost on time.

My question is why do we describe "ability" in different ways than "agility". For someone to say that a project has low agility or low ability isn't as effective as completely negating it. When describing a state of something wouldn't it be more effective to just negate the word entirely like "inability" yet the same negation doesn't seem appropriate with "inagility"?

Edit: I'm not trying to invent new words but I would like to be able to say that the "agility" is lacking. Someone pointed out that typically verbs are negated by "un-". I'm wondering how do they negate states in the medical field. Any suggestions?

Edit 2: I found a great paper on the agility of organizations. http://eprints.lse.ac.uk/30029/1/Collective_agility_(LSERO).pdf

Answer 1

The OED sets out several operational senses of dis-:

1. Undoing (disown)
2. Depriving (disarm)
3. Reversing (dishonest)
4. Imputing a negative feeling (disapprove)

The prefix un- (from Old English) almost always signifies a simple negation and often distinguishes itself from its Latin cousins in-, im-. So to be unmoral (i.e, to be amoral) is have no ethical guidelines, while to be immoral is be actively evil.

Likewise, there are differences in meaning from the prefix dis-. If you're unarmed, then you have no weapons, but if you've been disarmed, you once had them and someone has taken them away. (See 2 above.) The appropriations committee may unapprove a project, removing its funds and undoing a previous action for fiscal reasons, but if the members disapprove of the project, they actively dislike it. (See 4 above.)

Unfortunately, if the words are in use, there are no rules that will tell you the connotations. For instance, disapprove once had the additional meaning of disprove, but that meaning is obsolete, superseded by the sense of frowning upon.

Both prefixes are freely used to coin new words, and in that case, you're on your own. Unagile is not quick and not graceful, but what is disagile? Unagile or downright clumsy?

Answer 2

I'd definitely re-cast the sentence and use a current English word instead of inventing one. Sluggishness?

But to address the question, the Anglo-Saxon "un" would originally have applied to actions (verbs, mostly) like "undress" or "undo." The French "dis" would be for separation, splitting -- "disjoint," say. However, over the centuries these distinctions blur and combine.

Answer 3

Ability and Agility are different kinds of concepts. Ability is strictly a binary (yes/no) thing. You are able to do it, or you are unable to do it. You have the ability, or inability to do something. You should not, in good English, have a "low ability" to do something.

Agility is different. You can have it to a greater or lesser degree. Thus you can have a low level of agility, or a high level.