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)

Having the faculty of reason; endued with reason; rational.

a reasonable being

Just; fair; agreeable to reason.

* {{quote-news

, year=2012 , date=May 27 , author=Nathan Rabin , title=TV: Review: THE SIMPSONS (CLASSIC): “New Kid On The Block” (season 4, episode 8; originally aired 11/12/1992) , work=The Onion AV Club citation , page= , passage=The episode also opens with an inspired bit of business for Homer, who blithely refuses to acquiesce to an elderly neighbor’s utterly reasonable request that he help make the process of selling her house easier by wearing pants when he gallivants about in front of windows, throw out his impressive collection of rotting Jack-O-Lanterns from previous Halloweens and take out his garbage, as it’s attracting wildlife (cue moose and Northern Exposure theme song).}}

Not excessive or immoderate; within due limits; proper.

a reasonable demand, amount, or price

Not expensive; fairly priced.

$20 a bottle is very reasonable for a good wine at a restaurant.

Satisfactory.