The tourist protagonist
The tourist is a contemporary person in a jacket, dismayed by the past on the reader’s behalf. She notices sexism as if she has read about it, speaks of trauma in a vocabulary her neighbours could not use, and is shocked by cruelty her whole life would have taught her to expect. Readers may like her. They do not believe her. She makes the century a theme park she is visiting.
Belief is the contract. A mind is made of the sermons it has heard, the jokes that were allowed, the punishments it has seen land on someone else. You can mark a character as unusual. You cannot mark them as transported from a seminar. Unusual people in 1640 were unusual in 1640’s materials.
Resistance is historical
People have always refused. They ran, lied, pleaded scripture, used a patron, exploited a contradiction in the law, performed obedience and did otherwise, loved in secret, kept a skill that made them hard to discard. Those are period tools. A speech about equality, phrased as a later century would phrase it, is not one of them.
Give the refusal a local lever. She knows the will is unsigned. He can claim benefit of clergy. She has a cousin in the guild. The interest of the scene is the lever working or failing, not the announcement that the system is wrong. The reader can see that it is wrong. The character has to survive it with the tools on the table.
Language is a century’s tool as well
Words such as trauma, gender as identity, racism as a named analysis, boundary, empowerment, are not neutral containers. They bring a way of seeing that your viewpoint may not have. Translate the feeling into the words they would have spent: melancholy, a bad conscience, a person’s place, the blood, the nation, honour, credit, sin, a woman’s portion. The feeling can be recognisable. The label should not be imported.
This is not an instruction to reproduce every cruelty unexamined, or to write slurs for flavour. It is an instruction not to launder the mind. If a character holds a belief you despise, let them hold it, and let the story make its cost visible. A cast of secret moderns, all gently disagreeing with their year, is a way of refusing to write history at all.
What the reader is owed
The reader is owed clarity about harm, not a narrator who winks that we know better. You can structure a book so that a cruel norm is felt as cruel — by showing who pays — without giving the paying character a lecture they would not have composed. Irony, consequence and a second viewpoint do that work more honestly than an anachronistic aria.
If you need a character who sees further than their neighbours, earn the sight. A wider reading, a stranger’s household, a conversion, a loss that broke the proverb they were raised on. Sight without a cause is the tourist again. Sight with a cause is a person.
Try this
Take a speech in which your protagonist explains what is wrong with their world. Replace the explanation with an action that uses a period lever — a law, a patron, a doctrine, a debt — and cut every word they could not have learned yet.