Classification of impediments depends on whether the bar prevents formation of the cause, completion of the cause, the ruling’s commencement, or its continuation. These are not interchangeable merely because each is called a barrier.
One type of option may prevent the immediate establishment of a contractual consequence, while another affects the persistence of an effect that has already arisen. If no ruling began, the issue of its continuation differs; if an effect was established, its cessation needs an appropriate basis.
Diagnostic method: Locate the timing of the obstacle: before the cause forms, before it completes, at the start of the ruling, or during its continuation. Classification should follow that distinction.