* Concrete vs. Abstract: A concrete noun refers to something you can touch or see (e.g., chair, tree, book). An abstract noun refers to an idea, concept, quality, or feeling (e.g., happiness, freedom, justice).
* "Letter" as an Abstract Noun: When "letter" refers to the written symbol representing a sound, it's an abstract concept. You can't physically touch the letter "A" itself, only its representation on paper or a screen.
Example:
* "The letter 'A' is the first letter of the alphabet." (Here, "letter" refers to the concept of the symbol itself.)
"Letter" as a Concrete Noun:
* "I received a letter in the mail." (Here, "letter" refers to the physical piece of paper with writing on it.)
So, "letter" can be both an abstract and a concrete noun depending on the context.