An example of formal operational thought would be imagining the outcome of a particular action that has yet to be undertaken. Formal operational thought, in general, involves the ability to think in the abstract, the ability to combine and classify items and the ability to use high-order reasoning skills.
Formal operational thought is the type of cognitive activity that occurs within the titular formal operational stage as articulated by Piaget's theory of cognitive development. According to Piaget, the formal operational stage begins at around age eleven. Another example of formal operational thought would be reasoning through word problems, which involve coming to conclusions about hypothetical situations that involve abstractions of physical objects. A key element of the formal operational stage is the ability to make an inference. Someone in this stage of cognitive development should be able to draw conclusions about things they have not actually experienced by considering information presented to them.
Piaget used a test called the 'third eye problem' to determine one's full transformation into the formal operational stage. Piaget asked children where on their body they would put an extra eye and why. Children around nine years old typically answered that the third eye should be located on the forehead. However, children in the eleven year old range typically suggested that a third eye should be placed on the hand for seeing around corners. This answer characterizes the abstract thinking and reasoning which characterizes the formal operational stage.