If it is necessary to do a particular thing, that thing must be done.
It is necessary to act fast.It is necessary to examine the patient carefully.2. used with 'for'You can say that it is necessary for someone to do something.
It was necessary for me to keep active and not think about Sally.It is necessary for management and staff to work together positively.Be Careful!If you use necessary in sentences like these, the subject must be it. Don't say, for example, 'She was necessary to make several calls'. Say 'It was necessary for her to make several calls'. However, in conversation and in less formal writing, people normally say 'She had to make several calls'.
See mustIf one thing is necessary for another, the second thing can only happen or exist if the first one happens or exists.
Total rest is necessary for the muscle to repair itself.Collins COBUILD English Usage © HarperCollins Publishers 1992, 2004, 2011, 2012