If you want to append a list to another list you could also use the "Join" function: Join[{a,b},{c,d}] = {a,b,c,d}

Actually it's a fundamental principle in Mathematica that functions shouldn't change their arguments. Instead, they return modified data:.

For example, this is a list:

In[1]:= a = {1, 2, 3}
Out[1]= {1, 2, 3}

This returns a new list which has 4 appended at the end ...

In[2]:= Append[a, 4]
Out[2]= {1, 2, 3, 4}

... but it does not change a:

In[3]:= a
Out[3]= {1, 2, 3}

The functions that do actually change variables are a tiny minority, and include = and := (obviously); +=, *= and similar ones such as ++, --; and finally AppendTo and PrependTo.

Regarding discoverability, once you get used to how Mathematica works, this behaviour will feel natural and you'll realize that it makes functions behave predictably. Some other languages have both variety, functions like Append and functions like AppendTo, for many tasks, and you'll always have to check the documentation to see what a given function does precisely.

Mathematica does not have this problem. Does, e.g., Sort[a] change the order of the elements in a? No, it doesn't, it just returns a new list with elements rearranged.

Some more reading: * http://mathematica.stackexchange.com/a/42270/12

If you are considering appending multiple times in a loop, check Sow and Reap instead.

Append appends an element to the list and returns the result. It does not modify the original list. It used to be that if you wanted to do that you would use list = Append[list element]. (And you still can.)

AppendTo came later. It actually modifies the list itself, so the Set is not required.

ok, this is crazy...........it appears that within the scope of a notebook you can only use append to set the last element of the notebook? I check and if this is a bug it was present in Mathematica 9 as well. I would have expected multiple calls to the Append function to be able to append additional items to the same original List - am I missing something?

myList = {"a"}
myList2 = Append[myList, "b"]
myList3 = Append[myList2, "c"]


{"a"}
{"a", "b"}
{"a", "b", "c"}