In Music. Complete. (1) Perfect cadence, an authentic or plagal cadence. (2) Perfect concord, a common chord in its original position. (3) Perfect Consonance, the consonance produced by the intervals fourth, fifth, or octave. (4) Perfect interval, one of the division of intervals. (5) Perfect time. An old name for triple time. [A Dictionary of Musical Terms]
The Perfect Interval is a Major Interval where the lower tone is found in the Major Scale of the upper tone as well as the upper tone is found in the Major Scale of the lower tone.
The Major Sixth to the right is Major as D is part of the Major Scale of F but F is not part of the Major Scale of D. Therefore it is not a Perfect Interval.
The Perfect Fourth to the lower right is Perfect because F is found in the Major Scale of C and C is found in the Major Scale of F.
Perfect Intervals may be a 1st, 4th, 5th and 8th.
"If the sympathetic condition of any physical organism carries a positive flow of 80 per cent on its whole combination, and a negative one of 20 per cent., it is the medium of perfect assimilation to one of the same ratio, if it is distributed under the same conditions to the mass of the other. If two masses of metal, of any shape whatever, are brought under perfect assimilation, to one another, their unition, when brought into contact, will be instant. If we live in a sympathetic field we become sympathetic, and a tendency from the abnormal to the normal presents itself by an evolution of a purely sympathetic flow towards its attractive centres. It is only under these conditions that differentiation can be broken up, and a pure equation established. The only condition under which equation can never be established is when a differential disaster has taken place, of 66 2/3 against the 100 pure, taking the full volume as one. If the 66 2/3 or even 100 exists in one organ alone, and the surrounding ones are normal, then a condition can be easily brought about to establish the concordant harmony or equation to that organ. It is as rare to find a negative condition of 66 2/3 against the volume of the whole cerebral mass, as it is to find a coincident between differentiation; or, more plainly, between two individuals under a state of negative influence. Under this new system it is as possible to induce negations alike as it is to induce positives alike." [Keely - Cure of Disease]
The intervening chord between the Diatonic and Chromatic systems, B, D, F. - This chord, which has suffered expatriation from the society of perfect chords, is nevertheless as perfect in its own place and way as any. From its peculiar relation to both major and minor, and to both diatonic and chromatic things, it is a specially interesting triad. F, which is the genetic root of all, and distinctively the root of major subdominant, has here come to the top by the prime 2. D, here in the middle, is diatonically the top of the major dominant, and the root of the minor subdominant; and on account of its self-duality, the most interesting note of all; begotten in the great genesis by the prime 3. B, the last-begotten in the diatonic genesis, top of the diatonic minor, middle of the dominant major, and begotten by the prime 5, is here the quasi root of this triad, which in view of all this is a remarkable summation of things. This B, D, F is the mors janua vitae in music, for it is in a manner the death of diatonic chords, being neither a perfect major nor a perfect minor chord; yet it is the birth and life of the chromatic phase of music. In attracting and assimilating to itself the elements by which it becomes a full chromatic chord, it gives the minor dominant the G# which we so often see in use, and never see explained; and it gives the major subdominant a corresponding A♭, less frequently used. It is quite clear that this chromatic chord in either its major phase as B, D, F, A♭, or its minor phase as G#, B, D, F, is as natural and legitimate in music as anything else; and like the diatonic chords, major and minor, it is one of three, exactly like itself, into which the octave of semitones is perfectly divided. [Scientific Basis and Build of Music, page 101]
"Not that you are perfect but that you would grow!" [Cayce 1800-28]