There are several synonyms for the phrase "incapable of," each of which describes a similar state of inability. One alternative phrase is "unable to," which suggests a lack of capability or competence in a particular area. "Incompetent" is another synonym, implying a total lack of skill or knowledge in a given field. "Inept" and "clumsy" describe a certain level of awkwardness or lack of finesse in performing a task. Finally, "impotent" can be used to convey a sense of powerlessness or ineffectiveness, either as an individual or in a particular situation. Regardless of the specific word chosen, all these synonyms describe a lack of capability or proficiency in some regard.