Patrice y Dan,
De nada amigos. I'm glad you are enjoying Light Speed as am I, and I agree the presentation is really good. I actually watched all 10 of the subjunctive videos, one after another. No brevity there, about 1hr. and 20 minutes. I hesitated to address Daran's question as I didn't feel I could provide the rule and guideline he wanted. Remember Gordon's comments regarding the rules in the first video? I saw your reply Patrice, and that there is another person seems right to me as in your comparison to your phrase in which there is only the one person. Also, there is that lack of certainty. "What one can" is vague and seems to fall into the uncompleted or pending action need for the subjunctive.