At once a voice arose among     The bleak twigs overheadIn a full-hearted evensong     Of joy illimited;An aged thrush, frail, gaunt, and small     In blast-beruffled plume,Had chosen thus to fling his soul     Upon the growing gloom.
A joyful song was sung by a thrush to displace the gloom.
mnli hypothesis: A joyful song was sung by a thrush to displace the gloom. premise: At once a voice arose among     The bleak twigs overheadIn a full-hearted evensong     Of joy illimited;An aged thrush, frail, gaunt, and small     In blast-beruffled plume,Had chosen thus to fling his soul     Upon the growing gloom.