Believing in progress does not mean believing that any progress has yet been made. That is not the sort of belief that indicates real faith.
This aphorism was published posthumously and first translated to English in 2006: A bilingual French/German edition was published in 1994 (Aphorismes, Joseph K. editors, translation by Guy Filion). The French translation goes like this:
Croire au progrès ne veut pas dire croire qu’un progrès s’est déjà produit: ce ne serait pas une croyance
The original German text is available online at The Kafka Project. Here’s the same aphorism in German:
An Fortschritt glauben heißt nicht glauben daß ein Fortschritt schon geschehen ist. Das wäre kein Glauben.
Here’s the story about those aphorisms as shared by Jim Finnigan on James Geary’s blog All Aphorisms, All the Time:
The original aphorisms, though known of and posthumously published but only partly, were discovered in a folder in an archive in the new Bodleian Library at Oxford University. It was evident from the care in which they were composed (carefully hand written, numerated and ordered on thin strips of paper) that they were meant to be read as a whole series. In the introduction and the concluding essay to the volume, the Kafka scholar Roberto Calasso gives context to these aphorisms and the period of their undertaking. They were composed by Kafka in 1917-18 during a convalescence and a time of relative ease (except for the torment of household mice), while he was living with his sister in the town Zürau. As the introduction states, the aphorisms, though few in number (just over a hundred), are a varied lot. Some are short and pithy, as we expect of the aphorism. But quite few run to paragraph length.