The poem first line opens with "A sudden blow," and interesting action that remains somewhat ambiguous even after multiple readings. The phrase has a general connotation of a story about to begin, something akin to "Once upon a time" or "It was a dark and stormy night" but much more sinister and foreboding, and much less telling spatially and temporally, which is suiting to the tale. This is not a dependent clause; there is no verb or tense to place the phrase in the past or present, although one is to assume the tale is to take place in the past based on the well-known titular characters. Neither is there a subject or object: blow to whom? from whom? with what? One could assume the following words, "the great wings," could answer at least some of these questions, but this is only if one reads the poem superficially.
"The sudden blow" is followed by a colon, suggesting that the following lines of poetry are to describe the nature of this blow, its origin, etc. Thus, the "blow" refers to the entire incident of Leda's rape and the destruction, among other things, that is begotten from it. On a broader historical scale, however this blow represents any number of pit-falls experienced by feminists and women of Ireland during the early 20th Century. With each seeming progression of the Movement, such as the Representation of the People Act amendment which granted all people over the age of 21 the right to vote, the Feminists would suffer yet another sudden blow, such as the Juries Act 1924 which restricted women's rights to serve on juries.
Unlike the more brutal images of helplessness and destruction, this opening line connotes some measure of empathy that is somewhat obscured under the barrage of violence that follows it. Here we may glimpse W.B. Yeats' possible intent in culminating sympathy for both Leda's and women's struggles in general.
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