Is there a semantic difference between “need not contain” and “do not need to contain”?

This question already outlines what the syntactic differences between “need not” and “do not need to” are. However, a discussion unfolded below this answer about the following quote from this document: […] In order to cause [the] preprocessor to be invoked, it is necessary that the very first line of the program begin with #. … Read more

I can say: “You shouldn’t have done this!” Can I say: “You had better not have done this!”?

Provided “should” and “had better” are near synonyms (stronger advice in “had better” than in “should” or in more formal “ought to”), I know I can say You shouldn’t have done this! But how about You had better not have done this! ? Answer as Peter Shor points out, you can say either of them, … Read more

You must and you have to

Michael Vince in "English Grammar in Context" explains in his examples "You must be careful" is a speaker’s personal opinion" while "You have to be careful" an outside opinion or rule" but with the first person there is little difference sometimes between "I have to go" and "I must go". So either can be used. … Read more

need only do / only need to do

As I understand it, all the sentences are fine. I can’t understand why in the second sentence we don’t say "need only to do", but in the third we do (only need to do). Could you explain it, please? It needs (that) good people to do nothing. (need=require (an ordinary verb)) For it, good people … Read more

General possibility personal experience can/could/may/might

Would a native BrE speaker use "may/might/could/can" when talking about both personal experience and general possibility in these examples? "Earthquakes can/could/may/might be frequent/dangerous. (Generally) "Earthquakes can/could/might (not "may") be frequent/dangerous here." According to "English Grammar in Context" by Michael Vince "can" is the only option when talking about a general possibility as in sentence 1. … Read more

Could not or wasn’t able to

This exercise is from Raymond Murphy’s "English Grammar in Use". It’s about the use of "could have done." "Read this information about Ken: Ken didn’t do anything on Saturday evening. Ken doesn’t know anything about machines. Ken was free on Monday afternoon. Ken was short of money last week. Ken’s car was stolen on Monday. … Read more

Didn’t do and could have done

I am trying to understand the grammar of the first sentence. Only the first sentence is correct but I don’t understand why the other sentences are not. "If he didn’t say "Hello", he couldn’t have seen you". "If he didn’t say "Hello", he couldn’t see you." "If he hadn’t said "Hello", he couldn’t have seen … Read more