According to the First Doctor, questions, indicative of curiosity, were "the beginning of wisdom, of knowledge [and] of understanding". When a species began asking questions, no matter what prompted their inquiry, they arrived at a new frontier for their society. This was an evolution of sorts, the Doctor suggested. Though the nature of the questions themselves varied according to circumstances, "no matter how trivial they might seem [...] they have an unsettling tendency to lead to further questions".
This exponential rise in curiosity, beginning in this form across "all species", commonly culminated in an exploration of grand ideas and profound thoughts, which the Doctor favoured calling the "great unknown". (AUDIO: The Invention of Death)
The oldest question in the universe was "Doctor who?" (TV: The Wedding of River Song) According to the Fifth Doctor, the "second-oldest question" was "Why did the chicken cross the road?" (AUDIO: The Second Oldest Question)
Questions were prohibited in Light City, except on Jubilee, as "questions lead to questions" and "questions lead to answers; answers lead to knowledge; knowledge leads to freedom; freedom leads to dissatisfaction; dissatisfaction leads to unhappiness." These included self-orientation questions and interrogative prepositions. This social crime was punished by personality revision, or by death. Witnesses to such behaviour were also revised. (AUDIO: The Natural History of Fear)