Presupposition universals refer to the idea that certain types of presuppositions are shared across all languages or are fundamental to human communication. These can include assumptions about the existence of entities, the validity of claims, or the shared understanding of language itself. While the exact nature and extent of these universals are debated, they highlight the commonalities in how humans structure their understanding of the world through language. 

Here's a breakdown of key aspects:

1. What are Presuppositions?

Presuppositions are background assumptions that are implied by a sentence, even though they are not explicitly stated. For example, the sentence "The king of France is bald" presupposes that there is a king of France. If there is no king of France, the sentence is neither true nor false, but rather lacks a truth value, according to some theories. 

2. Presupposition Universals: Examples and Explanations

• Existence Presuppositions:

  Many languages have constructions that presuppose the existence of the entities they refer to. For instance, definite noun phrases like "the cat" often presuppose the existence of the cat being referred to. 
• Shared Understanding of Language:

  A basic presupposition in communication is that participants are using language in a mutually understood way. This includes shared knowledge of vocabulary and grammar. 
• Presuppositions in Argumentation:

  Idealized presuppositions of argumentation include the assumption that all relevant arguments are considered, that persuasion is based on the strength of the argument, and that all participants are motivated to find the best argument. 
• Universals in Pragmatics:

  Presuppositions are a key part of pragmatics, the study of how context contributes to meaning. Some theories of pragmatics suggest that certain presuppositions are universal across languages because they are fundamental to human communication. 

3. Debates and Challenges:

• Scope of Universals:

  While some presuppositions seem universal, the exact scope and nature of these universals are debated. For example, the degree to which presuppositions project (or survive) under negation or in other sentence embeddings varies across languages. 
• Semantic vs. Pragmatic Approaches:

  There are different approaches to understanding presuppositions:

  • Semantic theories: treat presuppositions as inherent properties of sentences. 
  • Pragmatic theories: emphasize the role of context and speaker intentions in determining presuppositions. 
• Experimental Evidence:

  Research on presupposition projection, particularly from quantificational expressions like "none," provides mixed results, suggesting that the projection behavior of presuppositions is complex and may vary. 

In conclusion, while the concept of presupposition universals is widely discussed, it is important to recognize that the exact nature and extent of these universals are still being investigated and debated within linguistics and related fields.