This is an example of the "third conditional". A hypothetical situation: one that didn't happen, but *would have* if some factor or condition had been different (in this case if the incongruent elements been absent). The writer probably should have chosen the word "otherwise" over the word "generally", since two subsets are being compared ("otherwise"), rather than the general case ("generally") and some subset. Anyway, in case it helps, here's how I'd write the passage: "Humor, and therefore laughter, can happen when a person finds themselves in an unfavorable situation where incongruent elements are present. Without the incongruity, the person would feel only anger and/or fear. But the detection of incongruent elements allows the person to view the situation from a different perspective." That rewrite fixes a few problems, but it's still not quite right because it doesn't explain that it's the problem-solving process (or, at least, the recognition of ambiguity) that is at the psychological root of humor. It's also interesting (but possibly out of scope) that the vast majority of times people laugh is not because something is funny, but simply because it's a social habit.