According to Aristotle, knowledge differs from belief in the following ways:

1) Knowledge has to be true.

2) Knowledge has to be believed to be true.

3) Knowledge has to be believed for legitimate reasons to be true.

If any of those three conditions are not met, the information, though it may be true, is still only a belief rather than true knowledge.

What is it to know something? When does someone actually know something? What can be known? What distinguishes true knowledge from false knowledge? These are questions of epistemology.

There are three necessary conditions for knowledge.

Knowledge requires truth. You can't 'know that P' if P is false. You can think you 'know that P' when P is false, but you can't realy 'know that P' unless P is true. No matter how hard one believes, grass is not purple.

Knowledge requires you to believe it. To say that someone knows that P implies (among other things) that he believes that P.

Just because you believe that P, and P happens to be true, doesn't necessarily mean that you know that P. Consider a clock.
  • You look a and see that it reads 11:43
  • You believe that it is 11:43
  • It happens to be 11:43
  • The clock stopped last week at 11:43
Do you know that it is 11:43? Are you justified in this belief?

Justification is the most controversial part of knowledge requirements. There are two types of justification:

Some beliefs are useful because they will help you get ahead in life. These beliefs are pragmatically justified. From a practical point of view, they are good beliefs to have. This does not show, however, that those beliefs are epistemically justified.

Having justification does not mean that you have to belief it. It is quite possible (and common) that people have justifications for things that run counter to their beliefs.

It also takes more than a belief to be justified than just having justification for believing it. Imagine that you have substantial evidence for believing that Oswald shot JFK, yet you are a conspiracy freak that you don't believe it. One day, your gypsy aunt holds a seance in which you "speak" to the dead Oswald and thereby "discover" that he acted alone. On the basis of this experience, you believe that Oswald acted alone. You have believe that P, you have good reasons for believing that P, but those aren't the reasons on which you base your believe. The basis of the belief is on bad reasoning. Thus, in this case, it could be said that your belief is unjustified, even though the proposition that Oswald acted alone is one you have good justification for.

Do not confuse justification with justifying arguments. When asked if a belief is justified, the question is one of if its epistemically reasonable for that belief to be held. It is not a question of if an explicit justifying argument can be given.

By Philip James Bailey

The knowledge of God is the wisdom of man—
This is the end of Being, wisdom; this
Of wisdom, action; and of action, rest;
And of rest, bliss; that by experience sage
Of good and ill, the diametric powers
Which thwart the world, the thrice-born might discern
That death divine alone can perfect both,
The mediate and initiate; that between
The Deity and nothing, nothing is.

The Atlantean axis of the world
And all the undescribed circumference,
Where earth’s thick breath thins off to blankest space
Uniting with inanity, this truth
Confess, the sun-sire and the death-world too,
And undeflected spirit pure from Heaven,
That He who makes, destroying, saves the whole.
The Former and Re-Former of the world
In wisdom’s holy spirit all renew.

To know this, is to read the runes of old,
Wrought in the time-outlasting rock; to see
Unblinded in the heart of light; to feel
Keen through the soul, the same essential strain,
Which vivifies the clear and fire-eyed stars,
Still harping their serene and silvery spell
In the perpetual presence of the skies,
And of the world-cored calm, where silence sits
In secret light all hidden; this to know—
Brings down the fiery unction from on high,
The spiritual chrism of the sun,
Which hallows and ordains the regnant soul—
Transmutes the splendid fluid of the frame
Into a fountain of divine delight,
And renovative nature;—shows us earth,
One with the great galactic line of life
Which parts the hemispheral palm of Heaven;
This with all spheres of Being makes concord
As at the first creation, in that peace
Premotional, pre-elemental, prime,
Which is the hope of earth, the joy of Heaven,
The choice of the elect, the grace of life,
The blessing and the glory of our God.
And—as the vesper hymn of time precedes
The starry matins of Eternity,
And daybreak of existence in the Heavens,—
To know this, is to know we shall depart
Into the storm-surrounding calm on high,
The sacred cirque, the all-central infinite
Of that self-blessedness wherein abides
Our God, all-kind, all-loving, all-beloved;—
To feel life one great ritual, and its laws,
Writ in the vital rubric of the blood,
Flow in, obedience, and flow out, command,
In sealike circulation; and be here
Accepted as a gift by Him who gives
An empire as an alms, nor counts it aught,
So long as all His creatures joy in Him,
The great Rejoicer of the Universe,
Whom all the boundless spheres of Being bless.

I can say I know something, but how would I know I really knew it? A.J. Ayer attempted to answer this very question by identifying three necessary and sufficient conditions for someone (S) knowing a proposition (P)- firstly, that P is true; secondly, that S is sure that P is true; and thirdly, that S has the right to be sure that P is true. Simply put, this necessitates the justification of an objectively true, subjective belief for there to be knowledge- for something to be knowledge, it would have to be justified true belief.

The subjective component reinforces the objective component, and the objective component reinforces the subjective component. Ayer believed we could not have the one without the other. Plato, in his Theaetetus, makes a clear distinction between knowledge and unjustified belief. He gives the example of a jury who cannot convict a person they believe to be guilty as they have not enough evidence to convict them on. (He was also a rich aristocrat who loathed the democratic system of justice but that’s for somewhere else). Then we have ‘knowledge’ which implies correctness. We would never doubt knowledge, or claim a false proposition as knowledge. A belief is not always true and we would never say a conviction was knowledge. The third component, the justification, is what the rest of it depends upon. But ‘having a right to be sure’ is what many of the major arguments against Ayer’s definition, have been.

The major arguments against Ayer’s definition have been put forward by Edmund Gettier against the justification component of the definition but minor counterexamples have also been put forward to the second condition, the belief in what is true. In 1966 Colin Radford said it is actually possible to know without believing. The best way I have of understanding this is by using an example from Dostoyevsky’s beautiful novel Crime and Punishment. Raskolnikov is going to see Svridligaïlov- he takes a turning he would ordinarily have never thought of taking. Usually he would turn right to the direction of::: okay, i haven't read the book for a while. but today he turns left and, as he believes, by chance comes upon a dirty tavern where he sees Svridligaïlov in an upstairs window. Raskolnikov did not believe he knew to take this turning. But subconsciously he did believe. He did not remember Svridligaïlov telling him three times of the tavern where he would usually drink and pay a minor to sing for him, but the knowledge was engraved in his subconscious. So Raskolnikov knew, but he did not believe he knew. There may be better examples than this of knowing without believing, but it’s the one I find makes me understand it better. Luckily for Ayer, D. M. Armstrong put a counterexample against Radford’s by telling him he’s merely giving us something we already knew. A person can only know something if he on some level believes it. So what Radford is saying is no argument, it only reinforces Ayer’s definition. Even if someone does not believe a proposition is true consciously, he will have to believe it is true for him to know it, according to Ayer.

However, the main argument against Ayer is not whether conditions in the definition are necessary, but whether they are sufficient. Could it be that one fulfils all the conditions for knowledge, and yet still not possess knowledge? Edmund Gettier published an article in 1963 in which he argued that this is possible. His example involved two people, Smith and Jones, applying for the same job. The chairman of the company assures Smith that Jones will get the job (Jones is better qualified for the job, the chairman has known Jones since birth, &c.). Smith also knows a fact about Jones- that he has ten coins in his pocket. So from this Smith concludes that the man to get the job has ten coins in his pocket. It turns out that Smith gets the job. He checks his pocket and finds, much to his astonishment, that he has ten coins in his pocket. So did Smith know he would get the job? All three conditions for knowledge are met- the proposition that the man with ten coins in his pocket will get the job was certainly true. Smith did believe this proposition was true. Smith also had good reason (the right) to believe this was true. But nobody in their right minds, and truthfully, would say he knew this. It was merely a coincidence, that he had the justified true belief that the man who would get the job had ten coins in his pocket. The basis of his justification was in Jones’ pocket and not his own.

In response to Gettier's article, several measures have been taken to try and fix this definition. One approach has been to try to distinguish between reliability and unreliability in ways of collecting beliefs. It was the justification part of the definition that was the problem, the way people based their beliefs on other things and were justified in them. The solution to this problem has been given by Robert Nozick. He called it the ‘conditional theory of knowledge’ and with it he attempted to remove the problem of someone’s justification that is based on a reliable method acquiring a belief that is true, but where the method plays no part in its success. Basically it is a simple tweaking of the traditional analysis of knowledge. Nozick accepts the first two conditions i)P is true and ii)S is sure that P is true. To these he added two new conditions, in place of the ‘S has a right to be sure’ which he rejected, and attempted to expand. These two new conditions are iii)if P were not true then S would not believe P and iv)if, in changed circumstances, P were still true, S would still believe P.

I can thus conclude that more is needed in a definition of knowledge than justified true belief. This is my first argument for Ayer being a bit of a pretentious charlatan.

Knowl"edge (?), n. [OE. knowlage, knowlege, knowleche, knawleche. The last part is the Icel. suffix -leikr, forming abstract nouns, orig. the same as Icel. leikr game, play, sport, akin to AS. lac, Goth. laiks dance. See Know, and cf. Lake, v. i., Lark a frolic.]


The act or state of knowing; clear perception of fact, truth, or duty; certain apprehension; familiar cognizance; cognition.

Knowledge, which is the highest degree of the speculative faculties, consists in the perception of the truth of affirmative or negative propositions. Locke.


That which is or may be known; the object of an act of knowing; a cognition; -- chiefly used in the plural.

There is a great difference in the delivery of the mathematics, which are the most abstracted of knowledges. Bacon.

Knowledges is a term in frequent use by Bacon, and, though now obsolete, should be revived, as without it we are compelled to borrow "cognitions" to express its import. Sir W. Hamilton.

To use a word of Bacon's, now unfortunately obsolete, we must determine the relative value of knowledges. H. Spencer.


That which is gained and preserved by knowing; instruction; acquaintance; enlightenment; learning; scholarship; erudition.

Knowledge puffeth up, but charity edifieth. 1 Cor. viii. 1.

Ignorance is the curse of God; - Knowledge, the wing wherewith we fly to heaven. Shak.


That familiarity which is gained by actual experience; practical skill; as, a knowledge of life.

Shipmen that had knowledge of the sea. 1 Kings ix. 27.


Scope of information; cognizance; notice; as, it has not come to my knowledge.

Why have I found grace in thine eyes, that thou shouldst take knowledge of me? Ruth ii. 10.


Sexual intercourse; -- usually preceded by carnal; as, carnal knowledge


Syn. -- See Wisdom.


© Webster 1913.

Knowl"edge, v. t.

To acknowledge.

[Obs.] "Sinners which knowledge their sins."



© Webster 1913.
