The name applied in the General Instruction on the Roman Missal (GIRM) to the psalm after the first (Old Testament) reading in the 1969 revision of the Roman Rite of the Mass. Originally, the psalm was performed by cantor and assembly in alternation, in the following fashion: a cantor sang verses of the psalm, and the assembly responded to them with a fixed refrain. As the music became more elaborate, the refrain consisted only of the final part of the responsory and was called the repetenda. The musical and textual form was as follows: R, V1, R, V2, R, etc. Its liturgical function was that of a meditative assent to the preceding scriptural reading. Thus, the gradual and alleluia were originally responsorial chants. By the middle ages, the ancient responsorial psalm evolved into a highly stylized musical piece that was sung by the choir or cantor without any congregational response.
The 1969 revision of the Roman Rite of the Mass restored the ancient practice of singing the responsorial psalm as "integral part of the liturgy of the word." (GIRM 19). GIRM 20 insists that "as a rule the responsorial psalm should be sung." It goes on to explain that there are "two established ways of singing the psalm after the first reading: responsorially and directly. In responsorial singing, which, as far as possible, is to be given preference, the psalmist, or cantor of the psalm, sings the psalm verse and the whole congregation joins in by singing the response. In direct singing of the psalm there is no intervening response by the community; either the psalmist, or cantor of the psalm, sings the psalm alone as the community listens or else all sing it together" (GIRM 20). To reinforce the understanding that the responsorial psalm is "an integral part of the liturgy of the word," the General Instruction prescribes that the responsorial psalm "is sung or recited by the psalmist or cantor at the ambo" (GIRM 22).
[r. g. weakland/eds.]
"Responsorial Psalm." New Catholic Encyclopedia. . Encyclopedia.com. (January 20, 2019). https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/responsorial-psalm
"Responsorial Psalm." New Catholic Encyclopedia. . Retrieved January 20, 2019 from Encyclopedia.com: https://www.encyclopedia.com/religion/encyclopedias-almanacs-transcripts-and-maps/responsorial-psalm