Hegel's philosophy in general stands at the centre of modern Western thought. Hegel's system integrates major intellectual developments, such as the various streams of Enlightenment and Romanticism, into its own formidable synthesis. Hegel sees human history as a movement of consciousness towards self-conscious freedom and rationality. Hegel's lectures on aesthetics were delivered in Berlin in 1823, 1826 and 1828-9. According to Hegel, art fulfils an important function in giving sensuous form to a concrete spiritual content, but philosophy constitutes a higher mode of representing spirit. Hegel explains that these three general forms of art, symbolic, classical and Romantic, are realized in the specific arts of architecture, sculpture, painting, music and poetry. The collision of actions in modern tragedy does not rest on conflicts extrapolated or introjected from the ethical order but is accidental, though substantive moral ends may be engaged in a contingent manner.