Across languages, we find indefinites that trigger modal inferences. This article contributes to a semantic typology of these items by contrasting Spanish algun with indefinites like German irgendein or Italian uno qualsiasi. While irgendein-type indefinites trigger a Free Choice effect (Kratzer and Shimoyama 2002; Chierchia 2006), algun simply signals that at least two individuals in its domain are possibilities. Additionally, algun, but not irgendein, can convey that the speaker does not know how many individuals satisfy the existential claim in the world of evaluation. We contend that the two types of indefinites impose different constraints on their domain of quantification: irgendein and its kin are domain wideners (Kratzer and Shimoyama 2002), whereas algun is an ‘anti-singleton’ indefinite (its domain cannot be restricted to a singleton). This, together with the fact that algun does not require uniqueness, allows us to derive the contrast between irgendein and algun by using the pragmatic reasoning presented by Kratzer and Shimoyama.