Sentence:  The only material the linguist has to begin with are the <WSD>informant</WSD>'s grammatical utterances in the target language pronounced arbitrarily in a natural or assigned communicative situation or stimulated artificially by the investigator. 
Meaning of the word marked with <WSD> tags:  A native speaker who acts as a linguistic reference for a language being studied. The informant demonstrates native pronunciation, provides grammaticality judgments regarding linguistic well-formedness, and may also explain cultural references and other important contextual information.