when might may not be may

commentary

As sometimes I need to clarify when to use modal verbs 'may' and 'might', and as they are both so often interchangeable, I today discovered some examples of when it is usually

may rather than might, e.g. the planet Venus may be seen clearly in the night sky during this month | The seeds from the plant may grow up to 20 centimetres in length | Exceeding the quoted dose may cause drowsiness – i.e., for academic language to talk about the characteristics or behaviour of something,

and

might rather than may, is sometimes used to talk about what was typically the case in the past, e.g. During the war, the police might arrest you for criticising the king | Years ago children might be sent down the mines at the age of six | In the early 19th century a person might be sent to Australia for stealing as little as a loaf of bread,

in all of which examples 'may' and 'might' are not usually interchangeable.

We can use might or may for a possible situation, e.g. I may go to Ireland | I might go to Ireland, but only might when the situation is not real. For example, If I were Tom's parents, I might look for a better job – you are not in Tom's position, you will not look for a better job.

Other, more everyday examples include: 

may I leave now? | May I help you? | you may not leave now – for permission

might they go by bus? (or could) – for possibility in the interrogative form (may they would imply permission), rather formal.

Historically, 'might' is the past form of 'may', but that fact doesn't offer any help in clarifying any current day usage of these two modal verbs. *I do, however, tell my students to change 'may' to 'might' when using reported speech (I may move to Sydney = he said he might move to Sydney).