intensify: implies a strenghening or deepening of a thing or its characteristic quality: police ~ their investigation.


aggravate: implies an increasing of gravity or seriousness of sth already bad or undesirable: the problem has been ~ by neglect.


heighten: sug. a lifting above ordinary or accoustomed: special effects of the movie ~ the sense of horror.


enhance: implies strengthing or raising such qualities as desirability, value, or attractiveness: the shrubbery ~ the grounds of the estate.


intensify: 泛指加强深化，aggravate: 使(原本不好)更严重，heighten: 超越平常普通,  enhance: 使更理想有价值有吸引力.


记忆方法:  1）根据词性:      

         enhance褒义              aggravate贬义


         intensify和heighten可用在好或不好的情况。


         2） 首字母联想，HE And I，他和我-->二人胜一人-->强化。

         3）加强的意思是显著增加，如程度度量mean to increase markedly in measure or degree.