'understand the necessity' is correct and usable in written English.
You could use it when you are trying to explain that someone needs to comprehend the importance of something. For example, "It is important to understand the necessity of recycling to help the environment."
"We understand the necessity of the U.S.'s new measures," Motohisa Suzuki, who coordinates antiterrorism programs for Japan's Cabinet Office, said on Thursday.
And, above all, to understand the necessity of its freedom.
But first it has to find politicians who understand the necessity of hybridity.
First, someone in Micheletti's circle needs to help his interim government understand the necessity of managing its international public relations to help position itself for the coming negotiations.
He is said to understand the necessity for the Greeks to undertake spending cuts, but stressed the same austerity approach across Europe would simply lead to recession.
"I can't predict what's going to happen, but I think the army and its chief understand the necessity for Guinea of ending this incoherence," he said.
Benitez was more serious when questioned over whether the players understand the necessity for squad rotation, with characters such as Terry keen to play in every game.
All educators understand the necessity of assessment, but it is our obligation to do the minimum amount of testing necessary, and no more.
But while senior managers understand the necessity of change to cope with new competitive realities, they often misunderstand what it takes to bring it about.
Undergraduate students find it difficult to understand the necessity of transforming key competencies into meaningful knowledge with regard to self, academia and career development.
