The concept of "mistake" is antithetical to jazz's spirit of uninhibited creativity. But jazz, like any musical style, conforms to a system of rules and conventions; indeed, this is what defines the style—what makes it sound like jazz and not some other style. When a jazz solo is "outside," or "out," it bears little relationship to the underlying harmony. But paradoxically, musicians require extensive instruction to play this way: an incompetent improviser is not merely playing "out." A rule of thumb for the improviser: it's not a mistake if you play it twice. But would it be a mistake if you played it once?

Previous analyses of jazz focus on acknowledged masters of the style, for obvious reasons; but these offer little help in systematically studying errors. To rectify this, during the 2014–2015 academic year, I recorded and analyzed solos by jazz students at the University of Massachusetts. In this talk, drawing on analyses of these solos, I offer some thoughts on the jazz "mistake." My focus is on "tonal jazz," the predominant style of the 1920s through the 1950s and the first style learned by most students.

Some errors result from disruptions to the physical act of performance—for example, a finger slips and hits the wrong key. Even among beginners, these "errors of execution" tend to be relatively rare: beginners usually attempt to play only those things that they reasonably expect to execute. The difficulty of improvisation lies not in playing, but in conceiving what to play. Since execution errors are not unique to jazz improvisation, they are not my focus here.

Errors in the soloist's selection of notes and rhythms have no equivalent in performances of composed music. We can approach them by an analogy between the acts of speech and musical improvisation. The speech act is susceptible to two categories of error. "Competence errors" stem from a speaker's deficient knowledge of the language—for example, a child's use of "goed" for "went." "Performance errors" stem from the contingencies of actual speech: fatigue, speaking quickly or on a difficult topic, and so on. Performance errors affect language learners and native speakers alike. These two categories also apply to errors in improvised solos.
S.P. Corder, an early observer of competence errors, notes that "the learner is using a definite system of language at every point in his development"; it is simply that the learner's system is different from that of a fluent speaker (Corder 1967: 166). For competence errors in jazz improvisation, we can often infer the "definite system" that underlies a student's error. Furthermore, a student's error may be in perfect accordance with typical jazz pedagogy, but nevertheless come across as stylistically clumsy. Such an error reveals shortcomings in current pedagogical approaches. To diagnose competence errors more accurately, we can compare multiple solos from the same student: a persistent kind of error reveals a faulty system, rather than a momentary lapse.

Momentary lapses—"performance errors"—can arise even among soloists who have mastered the jazz style. In such cases, circumstances like a fast tempo, an unusual chord progression, or a momentary distraction cause a "deviation from normal competence" (Boomer and Laver 1973: 123): the soloist chooses an incorrect note or notes normally avoided. Most such errors involve miscoordinations of timing between the melody and the accompaniment. For example, in a "perseveration," a soloist persists with a harmony for too long, carrying it into the space allotted to the next chord. This is equivalent to a native speaker of English accidentally saying "black bloxes" in place of "black boxes" (Fromkin 1973: 244). This speaker perseverates the initial "bl" sound.

The counterpart to perseveration is anticipation, another linguistic error with clear equivalents in improvisation. A similar error is the "blend," where an improviser mixes the properties of adjacent harmonies. For example, the quality of one chord might be blended with the root of the next chord. But other errors have no direct linguistic equivalent. For instance, a soloist might briefly play in the wrong key.

These analyses lead to some broader claims. Jazz solos are sometimes viewed as musical "works," of a kind. But a proper understanding of improvisational errors requires that we view a solo as a series of actions made in a particular context, rather than as a work. The context includes local and large-scale conventions of jazz improvisation, jazz pedagogy, and the soloists' other solos. From the solo itself and the surrounding context, we infer the soloist's intentions and abilities to explain the error. The errors interest us not for their content, per se, but as artifacts of the underlying improvisational process. Indeed, given the nature of jazz, even an error-free solo might be best understood not as a work, but as an act.