Is it possible to have a project with no critical activities? I think so because the total float does not have to be $\displaystyle 0 $ for any of the activities. We know that total float is: $\displaystyle \text{Total Float} = TF(i,j) = LT(j)-ET(i)-t_{ij} $. In other words its true that:

$\displaystyle LT(i,j) - ET(i,j) \neq t_{ij} $ for any activity right?