both are same. there is difference only when u get into literature or technical or official documentation other than the script devnaagari and nastaliq. Hindi has sanskrit/sanskrit derived words while urdu borrows words largely from arabic and persian. In general day to day speaking, both are same. U know one, u automatically know the other. Just one or two words change in the entire sentence(if the sentence is simple one). if u can tell which are persian/arabic words and which are sanskrit words in a sentence u can tell the difference. But case doesnt solve here, urdu has accepted many sanskrit words as well. Hindi means 'of Hind'(Hind - india in arabic) so the language of india is hindi by that means and by the same meaning Urdu again is language of India. it was also known as lashkari zabaan(language of army camps) because it facilitated communiction between soldiers from different countries(turkey, india,arab, faras) etc. The grammar of hindi urdu is again naturally of indian languages with a few cases of influence from persian and arabic (for example sometimes i listen people say rain is coming and this is how arabs say it is raining). the whole thing originated here in India(undivided). All the words other than tough arabic/persian/turkish are indirectly from sanskrit/original/regional or south indian languge family. take for example chalna, milna, kodanaa, jaana, aana, bolna ... etc. all these are same or derived from sanskrit words ucant say that this is from urdu or this is from Hindi. I most humbly request u not try to differentiate the two. If someone says that this is urdu or this is hindi, the reason should be solely on the fact that either the script is different or there are words which are uncommon(or incomprehensible) in either Hindi speaking community or Urdu speaking community. Why can't Hindi have arabic/persian words too? when urdu literature can use rahasya, jeevan, jeevani etc.? bottomline is the, daily conversation language is understood in both the communities(Hindi and Urdu) properly. so here, i consider it foolish to say this is Hindi, this is Urdu in this regard, unless the words are uncommon or not understandable.