"much" is an intensifier, so use it when you think the difference is very large. Use -er for one-syllable words and two-syllable words ending with "y", and use "more" for other adjectives. Bob is richer than Sam= Sam has 1 million dollars, and Bob has 1.2 million dollars. Bob is much richer than Sam=Sam has 1 million dollars, and Bob has 10 million dollars. Jane is more intelligent than Bob= Bob has an IQ of 100, and Jane has an IQ of 105. Jane is much more intelligent than Bob= Bob has an IQ of 100, and Jane has an IQ of 150. EDIT: ninja'd by Taylah! :)

Much more+dangerous Much more+ time-consuming Much more+ annoying Much more+ selective Much more + jovial Much more+ responsible It basically just depends on the suffix of the adjective and the number of syllables. There are certain endings that sound weird when attached to -er, such as the examples above. You wouldn’t say jovialer, selectiver, responsibler, time-consuminger, annoyinger, or dangerouser. You’d just initiate these expressions with “more”. The main reason why you’d use “more” is because these adjectives have more than one syllable and the suffix is not “y”. Words that don’t need “more” are nice (nicer), pretty (prettier), easy (easier), big(bigger), short (shorter)... The main reason why you’d use -er is because these adjectives have one syllable.

Much more sounds a bit redundant. I would only use much or more but not together. Examples: He has more tea than she does. Bill Gates has much money. (Much = a lot of)....Bill Gates has a lot of money.