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In his reply to Clarke?s third writing, Leibnizcontends that ? ? Ceux quidonnent dans ces sortes de fictions, ne sauroient répondre a ceux quiargumenteroient pour l?eternité du monde (GP VII,373).? The fictional character of a notion is also presented as an objection toa variety of philosophical doctrines; for example, Cartesian doubt is afictional attitude that leads to a paralogism that puts into question theexistence of corporeal things (GP IV, 356; VE N 3129). Naturally, occultqualities are also instances of fictitious entities that have to be rejected(for example, C 11-12). But this apparently disqualifying attitude againstfictions as a reason to reject certain theses on behalf of Leibniz can becontrasted with his admission of the fruitful use of fictions in twodisciplinary areas, that is, Mathematics and Law. A well-known mathematicalexample is that of infinitesimals, since these fictions are ??utiles et fondées en réalité (to Varignon, April 14, 1702).? but it is not the only one (forinstance, in algebra and other methods to resolve mathematical problems, A VI,iii, 523). As a jurist, Leibniz was well aware of the use of legal fictionssince the notion first appeared in Roman law (for example, the ?fictio legisCornelia? that is introduced to solve controversial cases involved intestaments), and they played an important role in his early work on conditionalrights. In effect, legal fictions are a form of procedure that allows theassumption of untrue facts to reach a juridical consequence that would not beenabled under the strict letter of the law, that is, fictitious conditions canbe used to solve controversial cases in testaments and other legal agreements,provided that they satisfy certain restrictions regarding their possibilitysuch as being compatible with other known facts (see for example A VI, I, 129;143; 392; 419). But the scope of these well-founded fictions is not limited tothese particular disciplinary domains. As Anne-Lise Rey has shown, fictionalstates of things such as those described in thought experiments, can beemployed by Leibniz in scientific arguments concerning the natural world (?L´expérience de pensée au péril de lafiction: Le cas de la correspondance entre Leibniz et Papin,? Revue d?histoire des sciences,vol. 66, No.2, pp.275-298).These heterogeneous examples of the cognitive rolethat fictions can play according to Leibniz suggest that the questionsconcerning their reference and other semantic issues cannot account for thecriteria by which to distinguish those fictions which Leibniz would regard aswell formed from those to be rejected. Otherwise the term would conceal an equivocal use. My purposeis to elucidate those criteria by analyzing the conditions that legal fictionsfulfill as well as the cognitive faculty involved (the imagination), and thetype of object it can entertain (abstractions) more generally, in order to elucidate to what extend non-denoting elements may besaid to provide truthful claims according to Leibniz.