What is an antonym prefix for the capable?

There isn't a single prefix that consistently creates an antonym for "capable". However, there are several prefixes you can use depending on the specific context and nuance you want to convey:

General Antonyms:

* In-: Incapable (lacking the ability or skill)

* Un-: Uncapable (less common, but sometimes used)

* Im-: Incompetent (lacking the necessary skills or qualities)

* Dis-: Disable (to make incapable)

Other Options:

* Ineffective: Not producing the desired results.

* Inefficient: Not using resources well.

* Unskilled: Lacking the necessary training or expertise.

* Powerless: Lacking the strength or authority.

The best prefix or antonym to use will depend on the specific situation and the meaning you want to express.