Which theological concept is Arminius best known for promoting?

Arminius is best known for promoting the concept of hypothetical universalism. This theological approach suggests that while God's grace is available to all people, it does not guarantee that all will accept that grace; thus, the possibility of salvation is extended to everyone. Arminius emphasized human free will and the belief that individuals have the capacity to choose or reject God's offer of salvation. This stood in contrast to the more deterministic views of predestination typically associated with Calvinism, specifically the idea that God elects certain individuals to salvation while passing over others. Hypothetical universalism maintains that God's willingness to save is universal, even if not all people ultimately receive that salvation. This concept significantly contributed to the development of Arminian theology, which focuses on free will and the universality of God's grace.