The 5th Dimension, which formed in 1965, were riding high on the success of their first No. 1 hit, "Aquarius / Let the Sunshine In," when they were offered a spot at the Harlem Cultural Festival.

But as they drew closer, The 5th Dimension drifted apart. "We talked about it at length,' said McCoo, "and we said, 'If we don't try to see where it can go, we'll never know.'" ...

The 5th Dimension’s earlier hits were basically show tunes that didn’t have musicals attached. Those songs radiate a chipper optimism that registers, at least to me, as a pure irritant.