Edward Said mentions "double perspective" in the essay "Intellectual Exile: Expatriates and Marginals," included in his collection Representations of the Intellectual. Originally delivered in 1993 as six Reith lectures on the BBC, Representations was published in book form in 1994.
The exact sentence reads:
Because the exile sees things both in term of what has been left behind and what is actual here and now, there is a double perspective that never sees things in isolation. (60)
Said frames this within a discussion of the exile's way of life, comparing them to Marco Polo, someone with a sense of the marvelous, who is "a traveler, a provisional guest." The intellectual always sees each thing they encounter in the new country in relation to something they left behind. This juxtaposition usefully sheds new light on both things; here, Said gives the example of human rights when compared to any kind of religious fundamentalism.
A related consideration of this double perspective is that it impels the intellectual to reconsider what they might once have seen as “a simple issue of judgment against an approved enemy.” By putting that judgment into a wider picture, the intellectual may now be required to take a secular position in regarding “all theocratic tendencies.”