The article reports on a longitudinal study of syntactic cross-linguistic influence (CLI) among L1 Polish learners
of L2 English and L3 Norwegian. The study mainly aimed to determine the influence of gradience in L1 on third language
acquisition. To this end, four syntactic properties were tested, two of which exhibit similarity between Polish and Norwegian
(subject-oriented possessive pronouns and adverb placement), and the other two – between English and Norwegian (definite and
indefinite articles). A group of 24 learners of Norwegian participated in an acceptability judgment task, which was administered
at three data collection times in all three languages. It aimed not only to determine the presence (and sources) of CLI, but also
to observe how gradience in L1 affects the assessment of equivalent properties in L3. In order to assess the role played by
gradience, the trilinguals’ performance was compared to that of a control group of English-Norwegian bilinguals. The data were
analyzed with mixed-effects ordinal logistic regression modelling, which showed statistically significant differences in the
ratings of articles between the two groups. We attribute this finding to gradient acceptability characterizing subject-oriented
pronouns and adverb placement in Polish, which is a potential source of non-facilitative CLI.