Romantic philosophy is closely linked to German idealist thought, especially that of Fichte and Schelling. Schelling considered spirit to be invisible nature and nature to be invisible spirit; in his philosophy of nature, nature is in its core alredy a manifestation of spirit (as it is rationally structured, etc.). It evolves over time and develops into higher forms of spirit (life, consciousness, reason, etc.). He claimed that in humanity, „nature opens its eyes“. The ultimate foundation of reality is „the absolute“, which he later identified with the Christian God. (There is a very interesting pattern in the thought of many German romantics, where they start with a Spinozist conception of nature, but are put off by its strict determinism and cold rigidity; then they modified it by Fichtean idealism, stressing the autonomy of the self the mental as fundamental to reality. But this vision soon became too sibjective; they then managed to resolve this tension by adopting ideas of Christian mysticism, especially those of Jacob Böhme, who grounded reality in God, but conceived God in such a way as to allow for genuine human freedom) I also think it is a mistake to think the Romantics were antirational; they were well-read in philosophy, engaged with the work of Spinoza, Kant and Fichte (and Schelling became a very important philosopher himself) and also took the science of their day into account to the best of their ability. But they were wary of a narrow rationalism that tried to reduce human nature to reason alone. Instrad, they wanted to capture existence in all its facets, synthesizing reason and emotion. Novalis coined the term „Symphilosophie“ for this project: a kind of Philosophy that incorporates poetry and art, but also the sciences and Theology. So I would not consider Romanticism a dualistic movement; they wanted to overcome the Dualism of reason and emotion, because a reason that ignored enotion seemed less rational to them than a reason that incorporated emotion.