Hello, fellas. Can you guess the differences between these two sentences: Tom is funny and Tom is being funny? One difference lies in the tense used in them. The first sentence uses simple present tense, while the second is written in present progressive tense. Due to the different tenses, the meaning they carry is not similar either.
According to Betty Schrampfer Azar, the use of simple present tense shows that an event or a situation exists in the past, present, and future. On the other hand, present progressive tense means that an event or a situation started in the past, is in progress when it is being said, and will probably end in the future.
(More on simple present tense and present progressive tense: https://englishtips4u.com/2011/10/09/engclass-simple-present-tense-positive/ and https://englishtips4u.com/2011/10/16/engclass-present-progressive-tense-positive/)
Present progressive tense may also be used with an adjective. The pattern is am/is/are being + adjective. It expresses someone’s temporary and uncharacteristic behaviour. However, only some adjectives can be used with such pattern: bad (ill-behaved), careful, cruel, fair, foolish, funny, generous, good (well-behaved), illogical, impolite, irresponsible, kind, lazy, logical, loud, nice, noisy, patient, pleasant, polite, quiet, responsible, rude, serious, silly, unfair, unkind, and unpleasant.
Based on the explanation above, in the first sentence Tom is known to be a funny person on a daily basis. On the contrary, as described by the second sentence, funny is not his characteristic.
1) Bill is generous.
This sentence means that generosity is Bill’s characteristic behaviour.
2) Bill is being generous.
In this example, Bill is said not to be generous in his daily life.
Betty Schrampfer Azar, Fundamentals of English Grammar: Third Edition
Betty Schrampfer Azar, Understanding and Using English Grammar: Third Edition