Assert facts, but not opinions.

Assert facts, including facts about opinions—but do not assert the opinions themselves'. By " fact" we mean "a piece of information about which there is no serious dispute." For example, that a survey produced a certain published result would be a fact. That there is a planet called Mars is a fact. That Plato was a philosopher is a fact. No one seriously disputes any of these things. So we can feel free to assert as many of them as we can.

By value or opinion, ^[1] on the other hand, we mean "a matter which is subject to dispute." There are many propositions that very clearly express values or opinions. That stealing is wrong is a value or opinion. That The Beatles were the greatest band in history is an opinion. That the United States is the only country in the world that has used a nuclear weapon during wartime is a fact. That the United States was right or wrong to drop the atomic bomb over Hiroshima and Nagasaki is a value or opinion. However, there are bound to be borderline cases where it is not clear if a particular dispute should be taken seriously and included. ^[2]

When we discuss an opinion, we attribute the opinion to someone and discuss the fact that they have this opinion. For instance, rather than asserting that "The Beatles were the greatest band ever", locate a source such as Rolling Stone magazine and say: "Rolling Stone said that the Beatles were the greatest band ever", and include a reference to the issue in which that statement was made. Likewise, the statement "Most people from Liverpool believe that the Beatles were the greatest band ever" can be made if it can be supported by references to a particular survey; a claim such as "The Beatles had many songs that made the UK Singles Chart" can also be made, because it is verifiable as fact. The first statement asserts a personal opinion; the second asserts the fact that an opinion exists and attributes it to reliable sources.

In attributing competing views, it is necessary to ensure that the attribution adequately reflects the relative levels of support for those views, and that it does not give a false impression of parity. For example, to state that "according to Simon Wiesenthal, the Holocaust was a program of extermination of the Jewish people in Germany, but David Irving disputes this analysis" would be to give apparent parity between the supermajority view and a tiny minority view by assigning each to a single activist in the field.

It is not sufficient to discuss an opinion as fact merely by stating "some people believe...", a practice referred to as "mass attribution". ^[3] A reliable source supporting that a group holds an opinion must accurately describe how large this group is. Moreover, there are usually disagreements about how opinions should be properly stated. To fairly represent all the leading views in a dispute it is sometimes necessary to qualify the description of an opinion, or to present several formulations of this opinion and attribute them to specific groups.

A balanced selection of sources is also critical for producing articles with a neutral point of view. When discussing the facts on which a point of view is based, it is important to also include the facts on which competing opinions are based since this helps a reader evaluate the credibility of the competing viewpoints. This should be done without implying that any one of the opinions is correct. It is also important to make it clear who holds these opinions. It is often best to cite a prominent representative of the view.

See also #Let the facts speak for themselves below and Wikipedia:Describing points of view, an essay on the topic.