Arrange the steps of the 1859 preface’s account of how a mode of production is transformed.

1. The productive forces develop within existing relations of production
2. Those relations, once suited to the forces, begin to obstruct them
3. The obstruction is experienced as a conflict between classes
4. An era of social revolution opens
5. New relations of production establish themselves and development resumes

Notice what the sequence does not contain: any moment at which people simply decide the arrangement is unjust. Marx locates the trigger in a mismatch between what a society can produce and how it is organised to produce it, which is what makes the account materialist rather than moral.