This morning, I set out to walk to the Philosophy Department. If asked my intention, I might have said that it was to reach the Department. And in actual fact I did reach it. Suppose, however, that as I was walking, my wife phoned me to inform me of a serious family emergency that required me to turn back, and that I did in fact turn back.
Here’s a puzzle. The family emergency in this (fortunately) hypothetical scenario seems to have frustrated my intention to reach the Department. On the other hand, surely I did not intend to reach the Department no matter what. That would have been quite wicked (imagine that I could only reach the Department by murdering someone). If I did not intend to reach the Department no matter what, it seems that my intention was conditional, such as to reach the Department barring the unforeseen. But the unforeseen happened, so my conditional intention wasn’t frustrated—it was mooted. If I intend to fail a student if he doesn’t turn in his homework, and he turns in his homework, my intention is not frustrated. So my intention was frustrated and not frustrated, it seems.
Perhaps rather than my intention being frustrated, it was my desire to reach the Department that was frustrated. But that need not be the case. Suppose, contrary to fact, that I was dreading my logic class today and would have appreciated any good excuse to bail on it. Then either I had no desire to reach the Department or my desire was conditional again: to reach the Department unless I can get out of my logic class. In neither case was my desire frustrated.
Let me try a different solution. I intended to reach the Department by morally licit means. The phone call made it impossible for me to reach the Department by morally licit means—reaching the Department would have required me to neglect my family. My intention wasn’t relevantly conditional, but included a stipulation as to the means. Thus my intention was frustrated when it became impossible for me to reach the Department by morally licit means.
The above suggests that our intentions should generally be thus limited in respect of means, unless the means are explicitly specified all the way down (and they probably never are). Otherwise, our intention wickedly commits us to wicked courses of action in some possible circumstances. Of course, the limitation, just as the intention itself, will typically be implicit.