What is the difference between a “hard” preparatory course and a “soft” preparatory course?

Passing the “hard” preparatory course means success in the preparatory course. Passing the “soft” preparatory course means that the student studied the preparatory course, was tested in it, and failed the course.
That is, if course X is defined as a “soft” preparatory course for course Y then, if the student took course X, sat the exam and failed the course, they can still study course Y. In a number of courses, adjacent preparatory courses are specified.
If course X is an “adjacent” preparatory course for course Y, registration for course Y is possible only if the student successfully studied course X before the current semester or is registered for X in the current semester.
Please note that a certain course can have both “hard,” “adjacent” and “soft” preparatory courses.
Full details can be found in section 1.2.3 of the regulations.