Universals vs. particulars refers to the philosophical debate concerning the nature of properties and their existence. Universals are general concepts or qualities that can be shared among multiple entities, such as 'redness' or 'beauty,' while particulars are individual instances or objects that possess these qualities, like a specific red apple or a beautiful painting. This distinction is central to understanding the development of medieval philosophy and scholastic thought, as thinkers grappled with how to reconcile these concepts within their theological and metaphysical frameworks.