Explain the concept of uncountable nouns.

Uncountable nouns, also known as non-count nouns or mass nouns, are nouns that cannot be counted or quantified as individual units. They refer to substances, concepts, or qualities that are considered as a whole or cannot be divided into separate parts.

Uncountable nouns do not have a plural form and are always used in the singular form. They are typically used with singular verbs and do not require an article (a/an) before them. Instead, they are often preceded by quantifiers such as "some," "any," "much," "a lot of," or "a little."

Examples of uncountable nouns include:

- Abstract concepts: love, happiness, knowledge, courage
- Substances: water, milk, coffee, sugar
- Materials: wood, glass, plastic, metal
- Food and drinks: bread, rice, cheese, tea
- Natural phenomena: rain, snow, sunlight
- Activities: swimming, dancing, running

It is important to note that some nouns can be both countable and uncountable, depending on the context. For example, "paper" can refer to a single sheet (countable) or the material as a whole (uncountable). In such cases, the meaning can be determined by the presence or absence of an article or quantifier.

Understanding the concept of uncountable nouns is crucial for proper grammar usage, as it helps in determining the correct verb agreement, article usage, and overall sentence structure.