Speaking of declarationist nominalism
Pope Francis laid another lump of jargon on us in his speech to the United Nations. He does this from time to time, perhaps most notoriously with Evangelii Gaudium's "self-absorbed promethean neopelagianism." I'm not sure why he lets these through without expansion, or even further comment. Maybe they're just meant as Easter eggs for people who like to overanalyze.
Such is the magnitude of these situations [of social and economic exclusion] and their toll in innocent lives, that we must avoid every temptation to fall into a declarationist nominalism which would assuage our consciences.
Well, obviously.
Nominalism as a philosophy (I write with the authority of some guy on the Internet) denies the existence of universals. (Though, apparently, nominalist kids these days deny the existence of abstract objects instead.) A universal is a property or characteristic that appears to be shared by multiple discrete objects; colors and shapes, like "redness" and "roundness," are common examples. (Wikipedia (or possibly Feldman) helpfully proposes the "Ness-Ity-Hood Principle" as a way of generating candidate universals. Add "-ness" or "-ity" or "-hood" to a word, and Bobness is your unclehood.)
A nominalist would say there's no such thing as "unclehood." (Part of the fun of being a realist is making nominalists say things that any sane person would giggle at.) Of less gigglity, perhaps, "humanity" isn't a real thing for nominalists, it's just a word we use to describe what we have in mind when we abstract something we notice humans have in common.
I'd say Pope Francis was referring to a degenerate form of nominalism, which shoots past "they're just words, not reality" and lands on "just words are reality." It's almost a form of sympathetic magic; if I invoke "care for the poor," then I am caring for the poor.
There is of course nothing wrong with invoking care for the poor (as long as you aren't doing it as part of a magic spell). But if a brother or sister has nothing to wear and has no food for the day, and you say to them, "Go in peace, keep warm, and eat well," but you do not give them the necessities of the body, what good is it?