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As books contained all manner of knowledge, the Tenth Doctor considered them the greatest weapons in the world. (TV: Tooth and Claw) Knowledge could be gained through education, though it was not realistic to expect any one individual to know everything. As such, knowledge could also act as a commodity, (AUDIO: The Renaissance Man) with power enough to tip the balance and even win a war. (AUDIO: The Devil You Know) The First Doctor differentiated knowledge from intelligence, describing the latter as one's ability to apply their own knowledge to a given situation. (AUDIO: Daughter of the Gods)

According to the First Doctor, "knowledge always snowballs." What always began as simple questions, "no matter how trivial they might seem", unavoidably led to further questions, and those to further questions still. As the Doctor observed everywhere, when a species began asking questions, they had arrived at a new frontier, inevitably leading to an exploration of the "great unknown". To the Doctor, this meant contemplating the biggest questions, thinking the grandest ideas and most profound thoughts. (AUDIO: The Invention of Death)

Someone whose expertise covered many different areas of interest was called a polymath. (PROSE: The Book of the War)

At one point in Earth history, during the Renaissance, it was entirely possible for one person to have the collected knowledge of humanity. Such people were exemplary of the Renaissance Man. In time, though, and indeed in the wider universe, it was more efficient for people to specialise, and develop an extensive breadth of understanding around a single topic. (AUDIO: The Renaissance Man)

The Thirteenth Doctor once claimed to have an understanding of "pretty much everything". (COMIC: A New Beginning)

Jephson wanted to gather all knowledge in the universe, doing so by draining it from the minds of visitors to the Morovanian Museum. This knowledge included historical, botanical and geographical information, as well as more practical knowledge, like Leela's hunting abilities. The Fourth Doctor defeated him by providing false knowledge, and inventing gaps in the data collected. (AUDIO: The Renaissance Man)

According to Leela, knowledge was only half the battle in a hunt, or in effecting capture. (AUDIO: Requiem for the Rocket Men)

According to Danna, some expertise could be taught which was beyond knowledge. She claimed to have "taught [Irving Braxiatel] everything he doesn't know", including how to how to exploit a dangerous situation, and how to read alien environments on arrival. (AUDIO: Soldier Obscura)

In the Unbound Universe, the Kareem believed knowledge was evil. (AUDIO: The Library in the Body)

The Abzorbaloff sought to absorb the Tenth Doctor's experience and knowledge. (TV Love & Monsters)