Reality

According to the Fourth Doctor, the differentiation of dreams from reality was an age-old conundrum. His own definition of reality did not include that which was imagined (AUDIO: The Crowmarsh Experiment) or illusory. (TV: The Ultimate Foe)

Zhuang Zhou, writing in the 4th century BCE, once pondered to himself whether he was a man who had dreamt he was a butterfly, or a butterfly now dreaming that he was a man. (AUDIO: The Crowmarsh Experiment)

According to the Seventh Doctor, reality was flexible, which explained how magic, which he defined as the use of words to affect materiality, was possible. (AUDIO: The Haunter of the Shore ^[+]Loading...["The Haunter of the Shore (audio story)"])

Someone else once asserted that there was only one certainty: cogito, ergo sum. Gideon Crane, believing himself to be the Doctor, challenged the real Eighth Doctor's conviction in his reality, saying that he could know only one thing: "All you know is that you are." (AUDIO: Minuet in Hell)

Accessing the Eighth Doctor's memories, Crane relayed something which had once been said to the Doctor:

"Everyone lives with their own personal reality. If my reality agrees with yours, we say we're both sane. If it doesn't, one of us is mad, or both."Gideon Crane

The Eighth Doctor, for his part, asserted that his memories must be indicative of reality, and sought to prove this with logical reasoning and evidence. (AUDIO: Minuet in Hell)

When the Sixth Doctor regarded the inside of the Matrix as not taking part in reality, the Valeyard criticised his one-dimensional view toward the concept. (TV: The Ultimate Foe)

According to both the Fourth Doctor and "Dr Stewart", when faced with two options, one ultimately became more certain of whichever reality one wanted more to believe in. For instance, Leela became more convinced of the false reality involving the Crowmarsh Institute after discovering that this world included Marshall, still alive and blissfully married to her. As she began to believe, false memories crept in which seemed to validate the lies she had been told. Jennifer became certain of the real world again when Leela spoke her daughter's name, which she could not possibly have known otherwise, and which also motivated Jennifer to return as she had promised her. (AUDIO: The Crowmarsh Experiment)

On being presented by the Dream Lord with two different dreams, the Eleventh Doctor and Rory Williams each became convinced that the scenario they preferred was reality, and the other a dream. Amy Pond decided that Upper Leadworth was a dream only after losing Rory there, at which point she no longer wanted to believe it could be real. (TV: Amy's Choice)

In some cases, however, reality was differentiated from fantasy, particularly when "cold, hard reality" was one's only option. (TV: The Girl Who Waited) The Twelfth Doctor had trouble distinguishing between the two, as reality and fantasy were "both ridiculous". (TV: Last Christmas)

According to the Third Doctor, the Atlanteans invented legends to "tame" reality when reality became unendurable. Later civilisations came to doubt whether their myths, gods and creatures were "real". The Doctor believed that they were, in part. (TV: The Time Monster)

A reality quotient, or RQ, was one measure of how "real" something was, with regards to causality. Objects native to the space-time continuum had a reality quotient of 1, where they could fully participate in events around them and make a difference. Objects with an RQ of 0.7 were still real enough to divert the course of history. (PROSE: The Crystal Bucephalus)

Whenever Amy Pond as a Ganger saw Kovarian during an adventure, this was, according to the Eleventh Doctor, "reality bleeding through". (TV: A Good Man Goes to War)

The Eleventh Doctor identified the 2020 Cwmtaff incident as a "temporal tipping point", explaining that it was not a fixed point in time. He claimed that such a tipping point would "change future events, create its own timeline, its own reality." (TV: Cold Blood)

The Fourteenth Doctor asked a human to examine two pictures of the Toymaker following a rupture in time that resulted in the creation of multiple versions of reality. (GAME: Double Danger ^[+]Loading...["Double Danger (game)"])

In most places affected by the Noodle Incident, the fabric of reality had already been knitted and unpicked many times ― and if the rumours were true, it had been "unravelled" too. (PROSE: Taste the Noodles of Dracula)