1.PLAIN

simple ▪ stark ▪ bare ▪ unequivocal

These words all describe statements, often about something unpleasant, that are very clear, not trying to hide anything, and not using more words than necessary.

plain used for talking about a fact that other people may not like to hear; honest and direct in a way that other people may not like:

The plain fact is that nobody really knows.

simple [only before noun] used for talking about a fact that other people may not like to hear; very obvious and not complicated by anything else:

The simple truth is that we just can’t afford it.

* Patterns

the plain/​simple/​stark/​bare/​unequivocal truth

a(n) plain/​simple/​stark/​bare/​unequivocal fact/​statement

a(n) plain/​simple/​unequivocal answer

2. ESSENTIAL

vital ▪ crucial ▪ critical ▪ decisive ▪ indispensable

These words all describe somebody/​something that is extremely important and completely necessary because a particular situation or activity depends on them.

essential extremely important and completely necessary, because without it something cannot exist, be made or be successful:

EX: 

• Experience is essential for this job.
• The police play a vital role in our society.

• essential or vital?

These words have the same meaning but there can be a slight difference in tone. Essential is used to state a fact or opinion with authority. Vital is often used when there is some worry felt about something, or a need to persuade somebody that a fact or opinion is true, right or important. Vital is less often used in negative statements: It was vital to show that he was not afraid. • Money is not vital to happiness.

crucial extremely important because a particular situation or activity depends on it:

It is crucial that we get this right.

critical extremely important because a particular situation or activity depends on it:

Your decision is critical to our future.

crucial or critical? These words have the same meaning but there can be a slight difference in context. Critical is often used in technical matters of business or science; crucial is often used to talk about matters that may cause worry or other emotions.

decisive of the greatest importance in affecting the final result of a particular situation:

She has played a decisive role in the peace negotiations.

indispensable essential; too important to be without:

Cars have become an indispensable part of our lives.

* Patterns

essential/​vital/​crucial/​critical/​decisive/​indispensable for something

essential/​vital/​crucial/​critical/​indispensable to something

essential/​vital/​crucial/​critical that…

essential/​vital/​crucial/​critical to do something

a(n) essential/​vital/​crucial/​critical/​decisive/​indispensable part/​factor

of vital/​crucial/​critical/​decisive importance

absolutely essential/​vital/​crucial/​critical/​decisive/​indispensable