Adjective

(en adjective)

Well grounded or justifiable, pertinent.

*{{quote-magazine, year=2012, month=March-April

, author=(Jan Sapp) , title=Race Finished , volume=100, issue=2, page=164 , magazine=(American Scientist) citation , passage=Few concepts are as emotionally charged as that of race. The word conjures up a mixture of associations—culture, ethnicity, genetics, subjugation, exclusion and persecution. But is the tragic history of efforts to define groups of people by race really a matter of the misuse of science, the abuse of a valid biological concept?}}

I will believe him as soon as he offers a valid answer.

Acceptable, proper or correct.

A valid format for the date is MM/DD/YY.

Do not drive without a valid license.

Related to the current topic, or presented within context, relevant.

(logic) Of a formula or system: such that it evaluates to true regardless of the input values.

(logic) Of an argument: whose conclusion is always true whenever its premises are true.

An argument is valid if and only if the set consisting of both (1) all of its premises and (2) the contradictory of its conclusion is inconsistent.

Adjective

(en adjective)

unsatisfactory; not acceptable

* {{quote-news

, year=2011 , date=December 16 , author=Denis Campbell , title=Hospital staff 'lack skills to cope with dementia patients' , work=Guardian citation , page= , passage="This shocking report proves once again that we urgently need a radical shake-up of hospital care," said Jeremy Hughes, chief executive of the Alzheimer's Society. "Given that people with dementia occupy a quarter of hospital beds and that many leave in worse health than when they were admitted, it is unacceptable that training in dementia care is not the norm."}}

(linguistics) not conforming to accepted usage