The Micrologus is a treatise on Medieval music

Medieval music

Medieval music is Western music written during the Middle Ages. This era begins with the fall of the Roman Empire and ends sometime in the early fifteenth century...

 written by Guido of Arezzo

Guido of Arezzo

Guido of Arezzo or Guido Aretinus or Guido da Arezzo or Guido Monaco or Guido d'Arezzo was a music theorist of the Medieval era...

, dating to approximately 1026. It was dedicated to Tedald, Bishop of Arezzo

Tedald, Bishop of Arezzo

Tedald , also known as Theodald, Theodaldus, Tedaldus, Tedaldo, or Teodaldo, was the forty-third Bishop of Arezzo from 1023 until his death....

. This treatise outlines singing and teaching practice for Gregorian chant

Gregorian chant

Gregorian chant is the central tradition of Western plainchant, a form of monophonic liturgical music within Western Christianity that accompanied the celebration of Mass and other ritual services...

, and has considerable discussion of the composition of polyphonic music.

This treatise discusses modified parallel organum

Organum

Organum is, in general, a plainchant melody with at least one added voice to enhance the harmony, developed in the Middle Ages. Depending on the mode and form of the chant, a supporting bass line may be sung on the same text, the melody may be followed in parallel motion , or a combination of...

 as well as free organum. The examples given are in two voices, set note-against-note, and the voices are frequently permitted to cross

Voice crossing

In music, voice crossing is the intersection of melodic lines in a composition, leaving a lower voice on a higher pitch than a higher voice...

. He advised against use of the perfect fifth

Perfect fifth

In classical music from Western culture, a fifth is a musical interval encompassing five staff positions , and the perfect fifth is a fifth spanning seven semitones, or in meantone, four diatonic semitones and three chromatic semitones...

 and minor second

Minor second

In modern Western tonal music theory a minor second is the interval between two notes on adjacent staff positions, or having adjacent note letters, whose alterations cause them to be one semitone or half-step apart, such as B and C or C and D....

, favouring instead the major second

Major second

In Western music theory, a major second is a musical interval spanning two semitones, and encompassing two adjacent staff positions . For example, the interval from C to D is a major second, as the note D lies two semitones above C, and the two notes are notated on adjacent staff postions...

 and perfect fourth

Perfect fourth

In classical music from Western culture, a fourth is a musical interval encompassing four staff positions , and the perfect fourth is a fourth spanning five semitones. For example, the ascending interval from C to the next F is a perfect fourth, as the note F lies five semitones above C, and there...

 (though thirds were also permitted).

One point of importance is his guideline for the occursus (meaning "meeting"), which is a predecessor of the later cadence

Cadence (music)

In Western musical theory, a cadence is, "a melodic or harmonic configuration that creates a sense of repose or resolution [finality or pause]." A harmonic cadence is a progression of two chords that concludes a phrase, section, or piece of music...

. An occursus occurs where two voices approach a unison

Unison

In music, the word unison can be applied in more than one way. In general terms, it may refer to two notes sounding the same pitch, often but not always at the same time; or to the same musical voice being sounded by several voices or instruments together, either at the same pitch or at a distance...

. He suggested that the unison should be approached either by contrary motion

Contrary motion

In music theory, contrapuntal motion is the general movement of two melodic lines with respect to each other. In traditional four-part harmony, it is important that lines maintain their independence, an effect which can be achieved by the judicious use of the four types of contrapuntal motion:...

 from a major third

Major third

In classical music from Western culture, a third is a musical interval encompassing three staff positions , and the major third is one of two commonly occurring thirds. It is qualified as major because it is the largest of the two: the major third spans four semitones, the minor third three...

, or oblique motion from a major second

Major second

In Western music theory, a major second is a musical interval spanning two semitones, and encompassing two adjacent staff positions . For example, the interval from C to D is a major second, as the note D lies two semitones above C, and the two notes are notated on adjacent staff postions...

.