General :: Using Sort And Uniq In Bash?

I have this file with the first lines as follows:

a
a
ability
able

[code]....

say the file is named file1.txt After i do the following:

sort file1.txt | uniq >> file2.txt

I expect that letter a would only appear once, not in two rows, word about would also appear only once. However, I can't seem to get that result using this. I also tried the sort -f file1.txt | uniq >> file2.txt but to no avail. I actually got file1.txt from a messier file using the -f option in sort command.