Applied Psycholinguistics, page 1 of 32, 2015 doi:10.1017 /S0142716415000351 Object pronouns, clitics, and omissions in child Polish and Ukrainian ROKSOLANA MYKHAYLYK Harvard University and Arctic University of Norway ALDONA SOPATA Adam Mickiewicz University Received: September 12, 2014 Accepted for publication: June 6, 2015 ADDRESS FOR CORRESPONDENCE Roksolana Mykhaylyk, Harvard Ukrainian Research Institute, Harvard University, 34 Kirkland Street, Cambridge, MA 02138. E-mail: roks.mykhaylyk@gmail.com ABSTRACT Polish and Ukrainian pattern together syntactically in allowing various omissions in the same dis- course settings, for example, when the referring element has been mentioned in a previous context. However, Ukrainian employs full object pronouns morphologically, whereas Polish uses clitics in the same environments. We exploit this contrast to compare the acquisition of clitics versus full pronouns, enriching previous accounts of omissions in child speech. The results of an elicited production exper- iment reveal that, in the two languages considered, 3- to 6-year-old children make no errors in direct object realization, but prefer to use null arguments up to the age of 5. It is crucial that there is no obvious difference between the acquisition patterns for clitics versus pronouns, which suggests that the morphophonological properties of direct objects are not primary predictors of object realization in languages that allow discourse-related omissions. The acquisition of referring expressions has been investigated extensively in a great number of studies (e.g., Allen, 2000; Gavarr´ o, Torrens, & Wexler, 2010; Gr¨ uter, 2006; Jakubowicz, M¨ uller, Riemer, & Rigaut, 1997; P´ erez-Leroux, Pirvulescu, & Roberge, 2008; Schmitz & M¨ uller, 2008; Serratrice, 2008). However, most of these studies focus exclusively on either subject referents or erroneous object omissions (also known as “nulls”). The present paper presents new research that offers a different perspective on the relatively well-known issue of reference- expression choice in child speech; specifically, we investigate the use of overt direct object (DO) types in two languages that allow null elements as a legitimate alternative. Slavic languages, in this case Polish and Ukrainian, allow a range of alternative structures. Opportunities for ellipsis are dependent on discourse accessibility. For © Cambridge University Press 2015 0142-7164/15 Author's copy