Homoiconicity (code and data having the same representation) is a commonly cited reason, which is key to the macro system in Lisp. Also commonly cited is the s

Homoiconicity (code and data having the same representation) is a commonly cited reason, which is key to the macro system in Lisp. Also commonly cited is the symbol type, which is also very useful in various AI contexts: http://www.cs.st-andrews.ac.uk/research/aisc http://www.cs.st-andrews.ac.uk/research/aisc This is not to say that you cannot do equivalent things in Java, but it is a lot easier in Lisp.