At the Indianapolis Museum of Art, “Hard Truths: The Art of Thornton Dial” honored an American original. The self-taught Mr. Dial, born in 1928 in rural Alabama, invented a personal, vernacular approach to collage: aggressively articulated, expressively—and beautifully—colored constructions incorporating a startling assortment of scavenged materials. Two decades of relief paintings, free-standing sculptures and drawings attested to Mr. Dial’s power. Their titles asserted deep convictions about ecology, civil rights, the role of women, and politics; their quirky materiality declared their affinity with the oddball objects in Southern "yard shows,” but no special pleading was required for the art or its author. Whatever the works’ lineage or motivations, whatever Mr. Dial’s history, “Hard Truths” was an impressive survey of first-rate works by a major artist. Period.