Sentence:  The two process types following from these assumptions, lenition processes, aiming at articulatory ease at the expense of perception, and <WSD>fortition</WSD> processes, resulting in articulatory difficulty in favor of better perception, were further modified by Dressler & Drachman (1977), as lenitions need not necessarily impede perception; similarly <WSD>fortitions</WSD> need not necessarily result in articulatory difficulty. 
Meaning of the word marked with <WSD> tags:  A sound change in which a consonant becomes more fortis.