Can 'might' mean the past tense of 'to be able' in 20th-century English?

Question

_{Source: p x, How Can You Represent Those People? (2013) by Abbe Smith, Monroe Freedman (Editors)}

Prominent criminal lawyer Edward Bennett Williams [ (1920-1988) ] once noted that, like other criminal lawyers, he took on difficult cases for unpopular clients, “not because of my own wishes, but because of the unwritten law that I might not refuse.” The lawyers in this collection could not refuse either. Moreover, they could not be prouder to champion the very worst of “those people.”

The 20th-century (20c.) meanings of (the past-tense Modal Auxiliary) might appear to contradict Williams's meaning above (the unwritten custom or maxim prohibits refusals to be based on unpopularity of the defendant), because they express possibility or suggestion, contrary to the decisive, dominating, and officious connotation that Williams needs (to emphasise the disapproval against refusal).

So did Williams use the incorrect Modal Auxiliary? I would have used (the Present Tense Modal Auxiliary) 'must'

Or I thought of this more charitable, forgiving but improbable possibility: Maybe Williams intended meaning of (the etymon of 'may') the Old English magen "to be able"? Then the bolded might would mean 'was not able to' which would accord with the context.

Answer 1

According to the Concise Oxford Dictionary, might is the past of may.

It occurs frequently in the bible, for example Galatians 2:19

For through the law I died to the law so that I might live for God

May can be used about possibility or permission. The excerpt from the passage you quoted does not mean "I was not able to refuse": it means "I was not permitted to refuse".

The use of may to request or give permission has declined in recent years (less than a century), and so the general usage of might has declined correspondingly. It is still widely used in certain idioms, for example "might I ask", "might I say" and "might I add": according to this NGram, usage of these idioms has actually increased in the past 20 years.

These expressions are examples of using the past tense to make a polite inquiry, as in "I wondered whether you would like to...", ie using might as the past tense of may.