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a great civil war, testing whether that nation, or any nation so conceived and so dedicated, can long endure.
here gave their lives that that nation might live
the unfinished work ... thus far so nobly advanced
the great task remaining before us
that cause for which they gave the last full measure of devotion
The words Lincoln uses to describe "a great civil war" in so compact a speech are mostly metaphor and metonymy thus difficult to pick out. The above quotations are all the descriptive references to the Civil War in Lincoln's speech. We'll talk about a couple of them.
In the first quotation, "a great civil war, testing whether that nation...," Lincoln describes the war in a metaphor as a "test" of the new nation's ability to endure. The quote explains that what is being tested is whether or not a nation (the U.S. or any other nation) that is conceived in and dedicated to the idea of government of, by and for the people can "long endure," or whether the republican democracy will be torn apart by conflicting ideologies. A metaphor states an implied comparison between two things that are not alike. In this case, a "war" is not like a "test," yet in the figurative language of metaphor, "war" is better understood by being compared to a "test."
The phrase "the unfinished work" might be analyzed as a metonymy that stands for and represents "the great civil war." A metonymy is a general concept that represents and stands for a more specific idea. For instance, news reporters sometimes say "President Obama's government" and sometimes say "the White House." "The White House" is a metonymy that is a general concept representing and standing for a more specific idea. The specific idea is President Obama's government. After the next election, there will be a new president, but the White House will still be the seat of that president's government. Thus reporters will have the choice between the specific "President Someone's government" and the general "the White House." Thus in this sense of the general substituting for the specific, "the unfinished work" can be called a describing metonymy of the Civil War.
Other descriptors state that the Civil War is the means by which the "nation might live," or continue, endure; is a "great task" to undertake that is inescapably "before" them and awaiting them; is a great "cause" that requires full and complete devotion: "the last full measure of devotion."