Concrete nouns and Abstract nouns

Concrete nouns refer to definite objects which you use at least one of your senses to observe. For instance, "chair", "apple", or "Janet". Abstract nouns on the other hand refer to ideas or concepts, such as "justice" or "hate". While this distinction is sometimes useful, the boundary between the two of them is not always clear. In English, many abstract nouns are formed by adding noun-forming suffixes ("-ness", "-ity", "-tion") to adjectives or verbs. Examples are "happiness", "circulation" and "serenity".