Note: the files in this directory contain an uncorrected pre-final draft of this paper. You should try to find one of the published versions if at all possible and read that instead. This version is intended only for those who have no access at all to a published version. The final edited and corrected version of this paper is published in the journal `Language'; the reference is: "Thematic Proto-Roles, Argument Selection, and Lexical Semantic Defaults", 'Language: Journal of the Linguistic Society of America', 67.3 (1990), 547-619. [This paper is also reprinted in 'Semantics: Critical Concepts', ed. J. Gutierrez-Rexach, Routledge. vol.IV (2003), 221-244.] NOTE: THIS PAPER SHOULD BE READ IN THE CONTEXT OF MY PAPER 'THE SEMANTIC CONTENT OF THEMATIC ROLES' (See main page for reference.) READING THIS PAPER WIHOUT READING THAT ONE TOO IS LIKELY TO LEAD TO MIS-INTERPRETATION OF THIS PAPER. Note on file format: The only electronic version of this paper I have exists only a very old version of postscript; the .ps files in this directory must be read with a postscript viewer (like ghostscript), not a .pdf viewer. If you go back to the main page and click on "(.psf)", that will take you to a directory with conversions of these files from .ps into .pdf by ps2pdf. Viewers for either format are likely to give you error messages when you try to open the files (telling you they are corrupted), but it's quite possible your viewer will then go ahead and display them anyway. If one format doesn't work for you, try the other one. If you are still unable to read either format, you need not bother writing to me asking for a different eletronic version, because I have none to give you. I cannot "fix" the files in this directory. What you should do in that event is try to find the 'Language' journal in your nearest university library. (If that library does not subscribe to 'Language', tell the librarian it should do so right away, and should order the back issues.)