Since Heubner's (1985) pioneering study, there have been many studies on (mis) use/ non-use of articles by L2 learners from article-less and article languages. The present study investigated how Persian L2 learners of English produce and interpret English definite descriptions and demonstrative descriptions. It was assumed that definite and demonstrative descriptions share the same central semantics of 'uniqueness', although they differ in the domain relative to which uniqueness is computed. While the book denotes the unique book in the discourse, that book denotes the unique book in the immediately salient situation. Persian has demonstratives and is partially marked for specificity, while English encodes definiteness. Persian L2 learners, due to lack of an equivalent for English definite marker 'the' in their language, use demonstratives as one of the compensating mechanisms to encode definiteness in definite descriptive contexts. A forced-choice elicitation production task and a picture-based comprehension task were used to examine Persian L2 learners' ability to distinguish definite and demonstrative contexts. The L2 learners were able to acquire both definite and demonstrative descriptions, but were more target-like regarding demonstratives than definite descriptions. The variability in choosing articles and demonstrative adjectives in one specific context (e.g. applying both the and that in contexts specific to the only or that only) shows that Persian EFL learners equate the demonstrative ān with both the and that. This also indicates that L1 transfer may determine the L2 learners' choices.