Block copolymer-containing composition and method of reducing pattern

A composition comprising:

• a component (A) being a block copolymer including a block PA bonded to one, or two or more blocks incompatible with the block PA and whose etching selectivity to the block PA is greater than one;
• and
• a component (B) being at least one polymer selected from the group consisting of a random copolymer and a homopolymer,
• wherein the polymer of the component (B) is compatible with at least one block other than the block PA within the blocks constituting the block copolymer of the component (A), and is incompatible with the block PA, wherein
• the etching selectivity of the polymer of the component (B) to the block PA is 1.1 or greater.