caption to keywords, minus grammar

Here is a start for you.

You will need to create a dictionary of words, I just created a text file with one word per line IE:

most 
much  
my
myself
neither
no one  
nobody
none
nothing
one
one another

NB: You will need to amend the code with the correct path to your dictionary!!!

The script will show up in the right click menu

#target bridge  
   if( BridgeTalk.appName == "bridge" ) { 
CreateKeys = new MenuElement("command", "Keys from Description", "at the end of Thumbnail");
}
CreateKeys.onSelect = function () {
   keysFromDesc();
   }

function keysFromDesc(){
///////////////////////////////////////////////////////////////////////////////////////////
// AMEND PATH TO SUIT!
var pronouns =File("~/desktop/pronouns.txt");
////////////////////////////////////////////////////////////////////////////////////////////
if(!pronouns.exists){
  alert("Dictionary does not exit " + pronouns);
  return;
}
pronounsList=[];
pronouns.open("r");
while(!pronouns.eof){
var line = pronouns.readln();
if(line.length>2){
line=line.replace(/^[ \t]+|[ \t]+$/g,'');
pronounsList.push(line+" ");
}
}
pronouns.close();
pronounsList=pronounsList.toString().replace(/,/g,'|');
var items = app.document.selections;
var items2 = new Array;
for (var a =0; a<items.length;a++){
  if(items.type == "file") items2.push(items);
  }
items = items2;

for (var i = 0; i < items.length; ++i) {
var item = items;
var md = item.synchronousMetadata;
var str = md.read("http://purl.org/dc/elements/1.1/","dc:description");
md.namespace = "http://ns.adobe.com/photoshop/1.0/";
md.Keywords = formatDesc(str);
}

function formatDesc(str){
str=" "+str+" ";
str=str.replace (/[\!\"\£\$\%\^\&\*\(\)\:\;\,\'\\\/]/g,'');
var rex = new RegExp (pronounsList,'gi');
var keys= str.replace (rex, '').split(' ');
return  ReturnUniqueSortedList(keys).join(';');
}

function ReturnUniqueSortedList(ArrayName){
var unduped = new Object;
for (var i = 0; i < ArrayName.length; i++) {  
unduped[ArrayName] = ArrayName;
}
var uniques = new Array;
for (var k in unduped) {
   uniques.push(unduped);
   }
return uniques.sort();
}
}