Peter Abelard is widely regarded as the father of Scholasticism, a philosophical and theological movement that dominated medieval thought.

Thomas Aquinas is famous for his Five Ways, a series of arguments that aim to demonstrate the existence of God through reason.

Siger of Brabant is known for his theory of double truth, which posits that there can be truths in theology that are different from truths in philosophy.

John Duns Scotus emphasized the importance of faith over reason, believing that certain truths can only be known through revelation.

William of Ockham is renowned for his principle of parsimony, which states that the simplest explanation is usually the best.

William of Ockham's principle of 'entia non sunt multiplicanda praeter necessitatem' (entities should not be multiplied beyond necessity) is a fundamental principle of his philosophy.

John Duns Scotus developed a theory of individuation that focuses on the concept of haecceity, which refers to the unique characteristics that distinguish one individual from another.

Thomas Aquinas sought to harmonize faith and reason, believing that they could coexist and complement each other.

Peter Abelard's theory of 'suppositio' analyzes how terms can function in different contexts and refer to different entities.

John Duns Scotus emphasized the role of 'lumen naturale' in human cognition, arguing that reason has the capacity to grasp certain truths independently of faith.

John Duns Scotus's theory of 'univocity of being' asserts that being is not equivocal but rather has a single, unified meaning that applies to all entities.

Thomas Aquinas proposed a hierarchical structure of beings, known as the 'scala naturae', with God as the supreme being and material objects occupying the lowest rung.

George Berkeley, an Irish philosopher, is known for his theory of 'esse est percipi', which posits that the existence of an object is dependent on its perception.

John Duns Scotus proposed the theory of 'esse in intellectu', which suggests that the essence of an object is determined by its mental representation rather than its physical existence.

Thomas Aquinas introduced the concept of 'transcendentalia', which are properties that transcend all categories of being and apply universally, such as unity, truth, goodness, and being itself.