In justified true belief it is said that for a person to know a fact it must be true, she must believe in it and she must be justified in believing it.
My question is: Is belief necessary? Why is the following not enough:
Your (1) and (2) are not enough. Here is an example: suppose I have excellent reasons to believe that the earth is round (I've seen photos, listened to lectures, etc.), and that it is in fact true that the earth is round, but nevertheless I do not believe it (because I'm irrational). Clearly this is not a case of knowledge.
There is a recent view, however, Knowledge First, that holds that knowledge cannot be analyzed in terms of belief (indeed, that it cannot be analyzed at all). But even on this view belief is a necessary condition for knowledge simply because knowledge entails belief.
According to Eric Schwitzgebel,
Contemporary analytic philosophers of mind generally use the term “belief” to refer to the attitude we have, roughly, whenever we take something to be the case or regard it as true. To believe something, in this sense, needn't involve actively reflecting on it: Of the vast number of things ordinary adults believe, only a few can be at the fore of the mind at any single time. Nor does the term “belief”, in standard philosophical usage, imply any uncertainty or any extended reflection about the matter in question (as it sometimes does in ordinary English usage). Many of the things we believe, in the relevant sense, are quite mundane: that we have heads, that it's the 21st century, that a coffee mug is on the desk. Forming beliefs is thus one of the most basic and important features of the mind, and the concept of belief plays a crucial role in both philosophy of mind and epistemology.
From this perspective the "belief" part of "justified true belief" is what is characterized as "true" and "justified" since we may have beliefs that are neither true nor justified.
It is not something that we, in addition, have to believe in. We already believe the fact but our belief might be incorrect. Now the question is whether that fact, that belief, actually is true and justified.
Reference
Schwitzgebel, Eric, "Belief", The Stanford Encyclopedia of Philosophy (Summer 2015 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/sum2015/entries/belief/.
Welcome George.
These conditions are not sufficient ('not enough') for knowledge because the fact may be true and she, X, may have justifiable reasons to conclude that it is true but those justifiable reasons may lead X only accidentally to conclude that it is true.
Suppose X is walking down a long, dark corridor. At the end there is a hologram of Y, her friend. Suppose that in the given conditions it is perceptually impossible to tell that she is seeing a hologram rather than her friend. In any case, she has visited her friend here often enough and there has never been a hologram before. So X has justifiable reasons to conclude that her friend is at the end of the corridor. How sceptically cautious are we going to require her to be ? By normal standards of evidence she is justified in concluding that her friend is at the end of the corridor. Now, suppose it is also a fact that her friend really is at the end of the corridor, behind and concealed by the hologram.
In this case (1) is true - her friend is at the end of the corridor and (2) is true - she is justified in concluding that her friend is at the end of the corridor. But because the perceptual causal chain is 'deviant' she doesn't know that her friend is standing there.
So (1) and (2) aren't enough for knowledge.
What you might choose to consider is the view, revived and powerfully argued for by Timothy Williamson, that belief is unnecessary for knowledge. The relation between knower and known does not include belief. This view is put forward in Williamson's Knowledge and Its Limits, ISBN 10: 019925656X / ISBN 13: 9780199256563. Published by OUP Oxford, 2002.
Another approach which can in certain versions eliminate belief from the conditions for knowledge is externalism. Here what matters is how a certain state of mind has come about; provided there is the 'right' causal connection between my state of mind and the external world, I can know without believing. If you ask me the French word for 'book', I answer 'livre'. There is an immediate disposition to say, 'livre', and this disposition is (let's assume) causally linked through memory to my learning French rather a long time ago. Of course, if you take a dispositional view of belief then to believe here just is to be disposed to answer 'livre'. But I do not think you are using this sense of 'belief'. And the idea of my having justifiable reasons for my answer simply doesn't apply. I haven't a clue how and when I learned that 'book' translates as 'livre'.
Why is belief necessary for justified true belief?
Well, let's take "belief" out. We get
justified true
This is not a grammatically correct sentence.
Let's take out, instead, "justified" and "true", in turn, and we get
justified belief
and
true belief
These are both perfectly fine phrases.
Belief then is necessary grammatically. Your elaboration of what belief means is just that - a further clarification of what it means to believe in this sentence. Generally it's taken as such in this sentence.
The thing is, when we're talking about knowledge in epistemology we are talking about personal, subjective knowledge. Looking at it that way, although all of the answers here are excellent, I think they miss the core point of the question (except, perhaps, Eliran's) - yes, the fact is true, and yes there is a justified reason to conclude that it is in fact true, but without the proper connection being made by the subject, and without the subject believing that it is in fact true, the subject would simply won't consider it as true. Not because it isn't true, and indeed someone else might actually acknowledge it as true, but without making the connection between the objective truthfulness of the fact and the subjective conviction of said truth, the subject won't consider the fact as acknowledged.
I think there are two distinct nuances in your question and I shall endeavour to address them both. The first is that facts are independent of belief so that by stating a "Justified true belief" we are speaking of a rational hypothesis the person has put forth and this has been borne out by facts and data. For example If I am asked to identify the object in front of me I believe it is an apple. At this point it is a belief since it has not been verified nor tested. It could be a genetically altered banana. After the facts and data show it to be an apple it is then a justified and true belief. It also ceases to be a belief as the data stands on its own without your belief. The second part is that the actual term "belief" tends to be nebulous regarding this concept. It is much easier to use the word "conclusion" for the second part. Going back to the apple analogy, you first say "I believe it is an apple" and after proving so, you then say "I am true and justified in concluding it is an apple". This eliminates your premise that belief is not needed when facts and data have provided a conclusion.
The answer is quite simple. It is the natural consequence of the definition of justified true belief and the requirements that a person must meet to have a justified true belief.
The requirements are:
1 The fact must be true.
2 The person must believe it is true.
3 The person must be justified in believing it is true.
Since your statements (1) & (2) only meet requirements 1 & 3, they are not enough (requirement 2 is missing) to have a justified true belief.
Because of logic and common sense. In the same way that it is necessary to have a dog in order to have a big dog, it is necessary to have belief in order to have justified true belief.
