In particular, convention attendance, the essential source of revenue for all of the groups, has declined.
Except that property taxes are an essential source of money for public schools.
His resentment served him well: his mastery of it was the essential source of his political appeal.
They are an essential source of timely and reliable information for the public.
If this NATO is "an essential source of stability in an unpredictable world," heaven help us all.
The performers were from the Argento Chamber Ensemble, which, under the direction of Michel Galante, has become an essential source of adventurous new music in New York.
Ansari's reporting describes an essential source of failure in Pakistan's counterterrorism and counterinsurgency campaigns: even where there is the will, there is often not a way.
Second, postdoctoral appointments, which are generally filled by researchers who have recently earned Ph.D.'s, are an essential source of candidates for permanent positions.
And today, as its 28 leaders declared in Lisbon, "the alliance remains an essential source of stability in an unpredictable world".
Public health, the Cinderella of the health service, is being recognised for what it is, the essential source of crucially needed preventive medicine, and is moving to the centre of health strategy.
"City AM has been a daily read for me since I came to London seven years ago and it's been an essential source of news and comment throughout my time at the Institute of Directors," May said.
