Benjamin opens this chapter by stating that the relationship between art and the masses has been changed by mechanical reproduction. He then goes to give a couple of examples of progressive reaction and backward reaction. I think these terms could be better understood by saying they are good and bad respectively. He then says that these judgements are linked to whether people enjoy their viewing experience, of how much pleasure they receive. To this end everyone has become an expert and so everyone has an opinion and he then suggests that anything new is met with aversion. He states:

Yet this progressive response is characterised by the fact that in it the pleasure of looking and experiencing is associated, directly and profoundly, with the stance of passing an expert judgement. (P26)

He then progresses onto comparing the viewing of film and paintings and their differences. Because film is more aimed at the masses than painting, because of its nature of being a mass viewing would then lead to the mass reaction. This is the new phenomenon in art (back in the 1930s, film has now existed for over a century so this needs to be viewed through early 20th century perspective) as viewing a painting was either solitary or within a small group. As he goes on to mention:

But although an attempt was made to bring painting before the masses in galleries and salons, there was no way in which the masses could have organised and checked on themselves in the context of that kind of reception. (P27)

So viewing film became more popular than viewing paintings or other art forms. Also, everyone has become an expert on films, of their likes and dislikes, which forms the mass reaction. Consequently, film has become the dominant art form, which most people can understand and relate to and by far the most accessible. We watch film on TV, computers, mobile phones, tablets and so on and can be watched pretty much anywhere.