Valid A  B From  Accepted Force Valid  Medieval

val·id
\\ˈva-ləd\\ adjective1. having legal efficacy or force; especially : executed with the proper legal authority and formalities
    a valid contract
2.
  a. well-grounded or justifiable : being at once relevant and meaningful
      a valid theory
  b. logically correct
      a valid argument
      valid inference
3. appropriate to the end in view : 

effective

    every craft has its own valid methods
4. of a taxon : conforming to accepted principles of sound biological classification
• va·lid·i·ty \\və-ˈli-də-tē, va-\\ noun
• val·id·ly \\ˈva-ləd-lē\\ adverb
Synonyms.
  , , , ,  mean having such force as to compel serious attention and usually acceptance.  implies being supported by objective truth or generally accepted authority
      a valid reason for being absent
      a valid marriage
   implies a basis of flawless reasoning or of solid grounds
      a sound proposal for reviving the economy
   may stress either weight of sound argument and evidence or lucidity of presentation
      the prosecutor's cogent summation won over the jury
   suggests a power to overcome doubt, opposition, or reluctance to accept
      a convincing argument for welfare reform
   stresses an immediate and crucial effect striking at the heart of a matter
      a telling example of bureaucratic waste

val·id
\ˈvalə̇d\ adjective
Etymology: Middle French or Medieval Latin; Middle French valide, from Medieval Latin validus, from Latin, strong, from valēre to be strong — more at 
1. 
 a. : having legal strength or force : incapable of being rightfully overthrown or set aside : sanctioned or authorized by sovereign temporal or spiritual power
  < a valid deed >
  < a valid covenant >
  < a valid title >
  < where a client has no valid ground for divorce — H.S.Drinker >
  < exempt from the natural laws which may be valid for lesser creatures — Ritchie Calder >
 b. : conforming to conditions essential to sacramental efficacy
  < the synod also declared that the only valid baptism was by immersion — K.S.Latourette >
2. 
 a. : well grounded or justifiable : applicable to the matter at hand : , 
  < the above theory was tested experimentally … and was proved to be valid — H.G.Armstrong >
  < particular grievances call … for the formulation of universally valid reasons why they should be redressed — Aldous Huxley >
  < find no valid evidence for such suspensions — W.R.Inge >
  < a valid argument >
  < a valid purpose >
 b. of an inference : correctly derived from its premises; specifically : true in terms of the logical principles of the logistic system to which the inference belongs
3. 
 a. : able to effect or accomplish what is designed or intended : , 
  < literary scholarship has its own valid methods — René Wellek & Austin Warren >
  < the written word was no longer a valid medium, the motion picture having supplanted it — Alexander Klein >
  < in finally finding her courage valid it had in the same moment vanished — Janet Terrace >
 b. : capable of measuring, predicting, or representing according to intention or design
  < if the results of university matriculation examinations are a valid test — B.K.Sandwell >
  — compare 
4. 
 a. : , 
 b. : , 
5. 
 a. of a taxon : based on distinctive characters of recognized importance : founded on an adequate basis of classification; also : validly published
 b. of the publication of a taxon : effective and accompanied by a description of the taxon or a reference to a previous description
Synonyms: 
 , , ,  may be compared with  in being applied to arguments, reasonings, principles, ideas which have such force that they compel acceptance. Both  and  imply that the force is inherent in the rationality of the thought apart from its presentation. A  argument or principle is supported either by objective truth or a generally accepted standard or authority
  < mathematical symbols, which are valid whether there is anything corresponding to them in nature or not — W.R.Inge >
  < charges always valid in every age and country — J.A.Hobson >
  although a  concept may have certain especially psychological limits
  < a “psychological fact” is valid for the person who holds it if for no other — F.J.Hoffman >
  , which may be applied to both persons and concepts, implies avoidance of fallacies, insufficient evidence, and hasty conclusions, and stresses solid foundation in fact or in reason or both, as well as the habit of clear and deliberate thought, often with an admixture of shrewed practical sense
  < much too sound a political thinker and too sagacious a party leader to rest his case upon abstract theory — V.L.Parrington >
  < good, sound reasons against the passionate conclusions of love — Joseph Conrad >
   and  apply to ideas (less frequently, to persons) compelling mental assent, but  stresses a force resident in the argument or reasoning, as inevitability or conclusiveness, as well as succinct and lucid presentation
  < the most cogent argument for freedom — man's tremendous innate variability — E.W.Sinnott >
  < the most cogent political comment of the year — G.W.Johnson >
  whereas a convincing argument, speaker, or book may convince by either sound reasoning or by skillful selection and presentation
  < there are other ways of making a thing … convincing … besides merely appealing to one's logic and sense of fact — Irving Babbitt >
   is often applied to fictional creations having the flavor of reality
  < in Aristophanes you have the convincing hurly-burly, the sweating, mean, talented, scrambling, laughing life of the Mediterranean — J.J.Chapman >
   suggests an immediate and crucial effect striking at the essence of the point, idea, or sentiment to be conveyed regardless of the validity of the cause
  < certainly makes some telling points … with a deftness that will disarm orthodox heresy-hunters — M.R.Cohen >
  < paused as if to edit his woes and select the most telling ones — Norman Mailer >