The phrase 'essential and necessary' is both correct and usable in written English.
You can use this phrase when describing something that is both vital and indispensable. For example, "Having access to clean water is essential and necessary for human survival."
Courage in peace is just as essential and necessary.
Current trends in architecture show that another systemic training of civil engineers is essential and necessary.
The thing is not to have as many ads as possible but to make them as essential and necessary as possible.
The "union of rational and irrational truth," symbols were the essential and necessary product of the unconscious, its "most important function".
Apart from monitoring the wear and the cutting forces, the knowledge of the developed temperatures during cutting process is essential and necessary.
The process of creating national academic standards should be revised to accord with the essential and necessary procedural requirements of standard-setting as described by the American National Standards Institute.
At the same time, however, Auriol wants to preserve the universality of universal concepts and their use in essential predications and necessary, scientific knowledge, and he thinks that his theory of concepts does just that.
This resulted in decreased access to essential diets and necessary micronutrients for vulnerable children and women.
The psychologists rated each item on a 3-point rating scale: "Essential", "Useful, but not essential" and "Not necessary".
"Regular and reliable information, which clearly spells out any alternative travel options is essential and, where necessary, additional services or stops should be provided e.g. extra services into Victoria".
If one is to conclude that formaldehyde is a "known" human leukemogen, one must assert not only that these hypothesized modes of action are conceivably true but that it is indeed known that one of them is true, for otherwise an essential and utterly necessary element of the causal conclusion is missing.
