In rhetoric, a premise is a statement of argument from which follows the conclusion of the argument. An argument is considered valid "if the truth of the premises logically guarantees the truth of the conclusion" (Internet Encyclopedia of Philosophy, "Validity and Soundness"). One example of a valid argument can be seen in the following since it is not possible for a conclusion to be false when the premises are true:
Either Elizabeth owns a Honda or she owns a Saturn.
Elizabeth does not own a Honda.
Therefore, Elizabeth owns a Saturn. ("Validity and Soundness")
Here, the two premises are that Elizabeth owns either a Honda or Saturn and that she does not own a Honda.
When looking at the premises of Jonathan Swift's argument in his satirical essay, "A Modest Proposal," we must keep in mind that it is satire. Since it is satire, the argument will actually have two groups of premises: The first group are the premises of the satirical argument, while the second group are the premises of the real social problem that influenced him to write the satire.
The first satirical premise is that Ireland is being overrun by impoverished persons, begging for charity, and those impoverished persons, being Catholic, are also overrun by children. The second satirical premise is that children of one year of age make a fine dish, as we see when he states, "I have been assured by a very knowing American acquaintance in London, that a young healthy child well nursed, is, at a year old, a most delicious nourishing and wholesome food, whether stewed, roasted, baked, or boiled." The conclusion is that if the impoverished begin both eating and selling this fine dish, then the population will be reduced and Ireland's economy will grow.
The real premise behind the satirical argument is that the land-owning Protestants of England have usurped the authority of the Irish Catholics and put them in a state of oppression. Since there are far more Catholics in Ireland than Protestants, the oppression is leading to devastating consequences. His premises of oppression are especially articulated towards the end of his argument when he begins listing other possible solutions for remedying the problem, such as "teaching landlords to have at least one degree of mercy towards their tenants."