# Explaining the need for two transistors in Not Gate

http://www.cs.bu.edu/~best/courses/modules/Transistors2Gates/

To teach myself transistor logic, but I have some questions on what I believe are unnecessary strucutres (most likely since I don't understand their physical need).

In the construction of the not gate, the site gives a combination of our input being split and connected to a $N$ transistor and $N^{-1}$ transistor such that the sink of $N^{-1}$ is the sourceo f $N$ and the output Z flows from between the two transistors

(The book didn't give a notation for specifying the normal and complementary transistors so I made my own, the behavior of N is if the input is 1, then it doesn't let the current flow,and $N^{-1}$ is complementary behavior)

Now I'm curious as to why we can't just have a single $N^{-1}$ transistor, with X as the input, and we take its sink to be the output. The sink will only have current flowing if X doesn't have charge, other wise it won't have current flowing if X does have charge.

Thats exactly the behavior of the not gate, so I guess the question reduces to: physically why do we need two transistors there?