G.A. Cohen, "Deeper into Bullshit"

Frankfurt's account of bullshit is only a partial account; he characterizes the essence of bullshit that comes from an intentional indifference to truth, whereas there is another kind of bullshit that needn't be intentionally produced. This other kind of bullshit is that which is unclarifiable. A rough test for this kind of bullshit is if affixing (or removing) a negation sign to the text under scrutiny does not affect "its level of plausibility".

Harry Frankfurt, On Bullshit

The essence of bullshit is indifference to the truth.