1724-1804 1758-1823 1762-1814 1770-1831 18thcentury 193 19thcentury contributionsinconceptoffreedomfichte contributionsinconceptoffreedomhegel contributionsinconceptoffreedomkant contributionsinconceptoffreedomreinhold georgwilhelmfriedrich history immanuel johanngottlieb liberty reason reinhold skepticism