A false dilemma is a type of informal fallacy in which there are said to be only a few limited alternatives, when in fact, at least one more option is possible. An example would be: "if the dog is not brown, it must be white."
In fact, the dog could be gray or black or many other colors. Therefore, such a statement would be a false dilemma. However, there are cases in which one can exhaust all options and therefore the dilemma is not false. The false dilemma is known by several other names, including: black-and-white thinking, bifurcation, denying a conjunct, the either-or fallacy and false dichotomy.