Causality

Causality was the relationship between cause and effect, and the concept that a cause must precede an effect in relative linear time. A causal nexus was a set of causes that influenced an effect, though Romana II also mentioned a "causality bubble" at one point. (AUDIO: Square One)

When the Doctor was young, he was taught by his tutor that "the universe is nothing but a functional chain of causality at every level, governed by the oldest and simplest laws." (PROSE: Longest Day)

The Eighth Doctor told Sam Jones that if he learned anything about future Gallifreyan history, causality could be damaged "beyond all conception." (PROSE: Alien Bodies) He later told Badar that he only made small changes to history to prevent causing any major damage to causality. (PROSE: Interference - Book One)

Bernice Summerfield stated that the creation of alternate timelines and other universes off of the main universe tended to "upset Causality's shopping trolly," which is why such deviations needed to be corrected. (PROSE: No Future)

The Eighth Doctor described anti-time as being as destructive to causality as antimatter was to space. (AUDIO: Neverland)

After the Eleventh Doctor freed the TARDIS from a space loop, he stated that there was no longer any danger of the localised time field imploding and ripping a hole in all causality. (TV: Time)

When asked to help save her younger self, Older Amy said, "You're asking me to defy destiny, causality, the nexus of time itself?" (TV: The Girl Who Waited)

Faction Paradox used technology to damage causality. (PROSE: Alien Bodies, Unnatural History, Interference - Book One)

The Edifice began affecting causality when it appeared above Gallifrey. (PROSE: The Ancestor Cell)

At the end of the universe, the laws of causality began to break down. (AUDIO: Singularity)