VERBS, AUXILIARY. May with a negativeMay with a Negative. Thus far Elizabethan and modern English agree; but when a negative is introduced, a divergence appears. In "I may not-come" may would with us mean "possibility," and the "not" would be connected with "come" instead of may; "my not-coming is a possibility." On the other hand, the Elizabethans frequently connect the "not" with may,1 and thus with them "I may-not come" might mean "I can-not or must-not come." Thus may is parallel to "must" in the following passage:--
Probably this disuse of may in "may not" (in the sense of "must not") may be explained by the fact that "may not" implies compulsion, and may has therefore been supplanted in this sense by the more compulsory "must."
“Yet I must not,
For certain friends that are both his and mine,
Whose loves I may not drop.