This study focuses on a native speaker of Chinese, in her 40's, who began to learn English in her late 20's when she emigrated to the United States. It was discovered that the subject was able to self-correct nearly every error she made in casual speech when the errors were pointed out to her after their commission. Furthermore, in nearly every case she was able to describe the grammatical principle involved. It is speculated that if second language users are able to apply such conscious rules when sufficient processing time is available, perhaps conscious knowledge is applied only when sufficient processing time is available. There is at least suggestive evidence that subconscious "acquired" linguistic knowledge (that is, internalized before puberty) is involved in ordinary unmonitored speech, while consciously "learned" rules are available to the second-language speaker only as a monitor. (Author/DB)