Francisco Costa's Calvin Klein Collection was a meditation on form. Not the female form, but, rather, geometric shapes. Many of the pieces looked as if they were draped and pressed over cubes, so that the short sleeves of a dress or the side panels of a jacket retained their three-dimensional echoes. The process gave Costa's soft, luxurious fabrics an airy sort of volume that was reinforced by a strict, cool palette of white, nude, icy lavender, and polar blue. When the idea was worked subtly it produced some lovely pieces, notably a white strapless dress with intricate pleats and folds at the neckline that didn't ignore the female body underneath. Too often, though, form trumped function, and the clothes looked boxy and squarea look that's hard to pull off if you're not a curveless 16-year-old. Fall's Calvin collection showed Costa in better form: intellectual, yes, but not at the expense of sex appeal. This season, he didn't quite hit the mark.