| Classification | Definition | Examples from Dorothy Dunnett's novels |
| Class 1 | Something happens which could not possibly have happened at that period in history. This includes the quoting, by a character, of poetry or prose which is not yet written (or translated, or available to them) at the time they quote it. | Maize grown in Africa pre-Columbus. |
| Class 2 | The characters use modern speech, but presumably there would have been an appropriate equivalent at the time | The Dame referring to 'Melodrama', and Lymond calling himself 'Neurotic' in the 1550s. |
| Class 3 | The author uses modern language to describe something which could have happened at the time, but would not have been described in those terms | Describing an 'Electric Storm', referring to something as being like a 'steel fence'. |