Yes, but you are forgetting that the NOT gate also has to convert a 1 to a 0, in which case it opens a drain to Ground. So your combinational logic is connecting Vcc to Ground, and as any electrical circuit does in such a situation you end up with a voltage gradient between the two, so on average your output would be 2.5 V in the given situation (depending on the placement of the connection it could be any value between 0 and 5V except the opposite connection would give the complement, causing it all to average out) Yes in theory you could operate a not gate without a drain, its just that the operation would be extremely unpredictable due to enviornmental variables. (and by extremely unpredictable, I mean completely. Due to enviornmental factors, there is no way to tell what value any given part of the circuit will have if you leave it floating [no inputs], as certain circumstances can cause it to even increase in voltage, so you can never trust a circuit node that does not have something actively giving it a value.) Edit: Also figured to clarify: on such an inverter, inputs of 0V-1V output ~5V; and inputs of 3.8V-5V output ~0V; Inputs of 1-3.8V give floating outputs which could be literally anything (general values, different components will have different specific values, but there will always be a large margin in the middle of undefined values)