All these manifestations of musical expression by popular singing may be executed by comparatively untrained individuals. Even some quite unusual and interesting harmonic progressions, the result of generations of experiment and selection, as for instance in Finland, Scandinavia, and among our Southern negroes, are not the result of individual training, but part of the general racial instinct for musical expression. The other classes of choral singing which we have enumerated above require considerable training of individuals in order to produce satisfactory results. In other words, whereas the folk-songs, dance, marching, and national songs were either the spontaneous expression of the people themselves or composed in the style of the people’s or folk-song whose chief centre of interest is the tune or melody while its harmonization is of secondary importance, the choral art-songs, to which belong part-songs, glees, madrigals, motets, cantatas, and all larger forms of choral music, employ a much more elaborate style of composition. The different voice-parts--soprano, alto, tenor, and bass--and their subdivisions often progress in rhythmic independence of each other. The voice-parts may enter the song at different times, in different sequence, in different metrical and rhythmical figures; they may sing different words simultaneously and therefore give different expression; sometimes one voice-part requires dynamic prominence, sometimes another, while the other voices subordinate themselves. All this requires that the individual singer must have a musical voice and true ear and a good sense of rhythm; that he should understand the rudimentary science of music and of notation; and that his eye should be able to recognize the symbols which indicate the pitch and time value of sounds and translate them instantly into the sounds themselves. Also, it requires that the individuals submit to the strictest discipline in obeying the directions of the leader. Only complete, intelligent, and instant obedience to the director on the part of every member of the chorus will produce good results. In other words, only team-work of the highest type secures mastery.