This article examines two key assumptions of models used to test theories of corporate capital structure - the trade off theory and pecking order theory. Specifically, it analyzes the assumptions of symmetric behavior and homogeneous coefficients. The researchers classify firms by industry and use spline regression to test the assumptions. They find that the symmetric adjustment rate assumption of the trade off theory is rejected, as firms adjust leverage faster when above the target. They also find the adjustment rate varies by industry, rejecting homogeneous coefficients. For the pecking order theory, they reject the symmetric behavior assumption at both the industry and overall level.