You're right, it's technically impossible (in my opinion...people who are FANTASTIC at meditation, though, will tell you otherwise...i'm just not good, so i pretend it is ) to have it clear.
Technically even then, your still thinking. Like (as alot of people do, such as myself) your usually focusing on your breath, etc. But I do get those feelings where I feel completely blank and numb when meditating sometimes.
A great way to waste time don't you think Oh yeah I'm moving to Rotorua in Easter which will be cool only 10 weeks in my sucky job and then I'll have to pay rent instead of living for free in my parents house lol but hey if I don't find a job I'll sign up to WINZ some call it bludging others like me call it money