Pretty 當副詞用時意為「相當，頗，很，非常」，可放在形容詞或另一副詞前面當修飾語。它是個非正式用字，通常用於口語及非正式場合，不可用於較正式的場合；正式場合須使用 quite 或 fairly。例如：
- Professor Smith comes from a fairly poor country but he is not poor. (史密斯教授來自一個相當貧窮的國家，但他並不窮) (正)
- Professor Smith comes from a pretty poor country but he is not poor. (誤)
如標題所述，pretty 不可用於否定句。例如：
- This type of smartphone isn’t very good, really. I don’t think I’ll use it again. (這款智慧型手機的確不是很好。我想我不會再用它了) (正)
- This type of smartphone isn’t so good, really. I don’t think I’ll use it again. (正)
- This type of smartphone isn’t pretty good, really. I don’t think I’ll use it again. (誤)
Pretty 與 much 和 well 固定搭配所形成的 pretty much 和 pretty well，是兩個不時可見的副詞片語，但意思與其字面相去甚遠，值得學起來。它們與另一片語 pretty nearly 都是同義詞，意為「差不多；幾乎」(almost)。例如：
- I can pretty much guarantee that he’ll be back in time. (我幾乎可以保證他會及時回來)
- It’s pretty well impossible for us to guess what he thinks. (我們幾乎不可能猜出他的想法)
- The work is pretty nearly finished. (這項工作差不多要完成了)