in Editing
Tense drift in long manuscripts
Past tense slides into present when a scene heats up, and nobody notices until chapter twelve. Here is why it happens and how to check.
Most novels choose a narrative tense early and keep it. Past tense is the more traditional choice; present tense has become common, particularly in some genres. Either works. The problem is not the choice but the drift, when a book written in one tense slips into the other without intending to.
Why drift happens
Tense drift is rarely a matter of not knowing the rules. It tends to happen for a few specific reasons.
Writers who read widely in both tenses absorb both rhythms, and a tense can creep in from whatever they were reading that week. A scene that feels urgent can pull the prose towards present tense, because present feels immediate. Revisions made months apart may be written in different moods. And a manuscript that began in one tense and was converted to the other almost always contains survivors, verbs that were missed in the change.
Long manuscripts make all of this harder to see. The writer reads in sections, and a slip on page 214 is invisible when you have not read page 213 for a week.
Legitimate tense shifts
Not every change of tense is an error. In a past-tense narrative, a character's general truths can sit in the present: "She had grown up in a town where everyone knows everyone." Dialogue is always in whatever tense the speaker would use. Flashbacks within a past-tense narrative often use the past perfect ("had gone") for a sentence or two before settling back into simple past.
A present-tense frame with past-tense memories is also a structure many books use. The key is that each shift has a reason and happens at a clear boundary.
The past perfect problem
A related drift affects past-tense narratives: overuse of the past perfect. When recalling earlier events, writers sometimes keep every verb in "had" form for pages. It becomes heavy. The usual approach is to use the past perfect to enter the flashback, shift to simple past for the body of it, and perhaps use the past perfect once more on the way out. Readers follow the change without needing every verb to signal it.
How to check
Reading aloud helps, because tense slips are easier to hear than to see. Reading the manuscript in a different format, such as printed pages or a different font on screen, can also make familiar text strange enough to notice problems.
A more mechanical approach is to search for common present-tense verbs in a past-tense book, such as "is", "are", "says", "walks", "looks", and check each hit outside dialogue. It takes time but catches a great deal. For a present-tense book, search for "was", "were", "said" and "had".
Copy-editors look for tense drift as a matter of course, and a clear note on the intended tense in the style sheet makes their job faster.
If a scene genuinely wants a different tense, consider making that a structural decision: a separate section, a marked change, something the reader can see. What works on purpose rarely works by accident, and readers can usually tell which is which.