; Depends on interpretationThe distinction between the two very much depended on which side you were on. If, like the Ulster Unionists and majority of British politicians you considered the Act of Union and Ireland's inclusion in the British Empire as constitutionally valid, then you would only accept political activity based on British Parliamentary practice as legal and constitutional - everything else would appear to be revolutionary and illegal. This would include the activities of The Citizen Army, Irish Volunteers, I.R.B., the Easter Rising, the refusal of the elected Sinn Feiners to recognise British rule, the activities of Collins and the I.R.A. etc.If however you considered British rule over Ireland to be an illegal occupation by force, and you believed that the victory of Sinn Fein in the elections of 1918 created a democratic and moral mandate for separatism, then you would regard the actions of the Provisional Government as completely constitutional rather than revolutionary.The fact that,in the end, Lloyd George's coalition government agreed to talks does rather suggest that they were pushed by world public opinion into at least accepting that Irish nationalists had the right to a degree of self-determination provided it didn't damage British interests too much - hence the terms of the Treaty.

The distiction is very valid as it is based upon the tactics used. Prior to 1916 the most supported form of nationalism was constitutional nationalism. Constitutional nationalists were those that did not support the Act of Union (1800) and fought for home rule. But they believed that home rule should be gained through parlimentary procedure and not through the overt use of force. During the time period in question this action was respresented by the Irish Party at Westminster and was led by John Redmond. Of course other well known constitutional nationalists were James O'Connell, Isaac Butts and Charles Stewart Parnell.

Revolutionary politics supported the idea that the British would not respond to constitutional measures and that only the use of force would get them to release their grip on Ireland. This was seen in the actions of groups like The Yound Irelanders, The Irish Citizens Army and of course The Irish Republican Brotherhood (IRB).

There is also the consideration of the philosophy of the organizations. Constitutional nationalist fought for Home rule. This was a separate Irish Parliament still subject to the British crown, whereas the revolutionary nationalists believed that nothing less then complete independence from the crown was acceptable.

It worth noting that the majority of the people of Ireland supported the constitional methods up to 1916. After the Easter Rising and the atrocities committed by the British army, in conjuction with the secret court martials and executions of the leaders of the rising, mass support shifted to the revolutionary nationalists leading to the virtual death of the Irish party and the rise Sinn Fein. However, after the end of the war for independence the majority support shifted back to peaceful measures of gaining more freedom and in the end it was a quiet act of government that separated Eire from the crown (speaking solely for The Republic of Ireland, of course).