Which characteristic defines symbols?

Symbols are fundamentally characterized as arbitrary because they do not inherently possess the meanings that we assign to them. The meanings of symbols are determined by cultural and social conventions, rather than by any natural connection to what they represent. For example, the word "tree" is just a combination of sounds or letters that we have collectively agreed upon to represent a specific concept; there is no intrinsic reason that this combination should denote a tree instead of, say, a rock or a concept.

In contrast, the other characteristics presented in the options do not accurately reflect the nature of symbols. While some symbols may seem necessary within certain contexts, they are not universally required—different communities may develop different symbols for similar concepts. Symbols do not always represent physical objects; they can also represent ideas, emotions, and abstract concepts, such as freedom or justice. Lastly, symbols can and do change over time as cultures evolve, allowing new meanings to emerge and old meanings to fade. This adaptability is a key aspect of how symbols function in communication.