What is an imperfect authentic cadence?

An imperfect authentic cadence is characterized by its resolution to a tonic chord (I or i) but with specific conditions that differentiate it from a perfect authentic cadence. In an imperfect authentic cadence, either the highest note in the final chord is not the tonic, or the bass does not contain the root of the tonic chord. This creates a sense of resolution while lacking the definitive assertion of the tonic that a perfect authentic cadence provides, where the tonic is in both the bass and the highest voice.

The other options describe different musical concepts. A cadence ending on the subdominant chord is not a resolution to tonic, thus does not fit the definition of authentic cadence at all. A parallel progression from IV to V is indicative of a harmonic movement but does not specify a resolution to tonic, which is essential in discussing cadences. Similarly, a suspended chord resolving to the tonic describes a specific harmonic event but does not align with the standard definitions of cadences needed for this context. Thus, focusing on the nuances of the resolution to tonic with certain voicing elements accurately defines the imperfect authentic cadence.