Allusions are the use of literary device that uses an indirect way of addressing an issue without the use of any direct reference. Martin Luther King in his now famous speech "I Have A Dream" talks of many allusions. One of these allusions is the excerpt provided in the question -
<em>"Five score years ago, a great American, in whose symbolic shadow we stand today, signed the Emancipation Proclamation."
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alludes to the Emancipation proclamation of President Abraham Lincoln in 1863. Saluting the effort of the then President, King alludes to the time when all slaves were freed by this. He also promises to continue to work for the same issue that President Lincoln had done.
