The issue of NPOV v. SPOV has been raised in a current Arbcom case. Whether or not it progresses, I'd like to check the following description of the difference between them, and confirm it's a fair description (or otherwise) since this is an issue which acts as a WP:COATRACK for other concerns and advocacies.
NPOV vs. SPOV: NPOV vs. SPOV is a conflict that can arise when scientific views on a matter exist, but are not the sole significant view.
In describing matters, we give each view on the matter its due prominence, or weight ("WP:WEIGHT"). When a view is 'mainstream', - ie, widespread, highly accepted by reliable sources, propounded by authoritative voices that themselves are well respected, and non-controversial (there is little authoritative dissent in reliable sources) - then this means it will usually have a significant prominence, or even at times be the sole view stated.
Scientific views often have this standing on subjects they touch upon. Therefore when articles touch on scientific matters, the most usual result is that the scientific view gains a high prominence, where relevant, in the description. In many cases this may end up being the sole significant view, in which case it is the sole view described. (eg, the sole significant view why rocks fall down, is in fact the scientific view - gravity. The sole significant view why people catch flu is the scientific view - micro-organisms.)
The critical factor is, we do not in fact give science this prominence just because "science says so" (SPOV), even though it may seem that way. We do it because the scientific view is the sole, or supermajority view on the matter in this instance (NPOV). In other words, although it may look as if we do it because "science says so", in fact we are doing it because it is also a neutral encyclopedic representation of the significant views, for this specific subject.
NPOV is mandatory in all cases. So although the two often agree, NPOV does in fact takes priority (in all cases on Wikipedia articles) when there is doubt. For this reason, when there is more than one significant view, we do not just state one view only, or disparage (or flatter) the alternative. Each is neutrally described and given its due weight, as is the balance and mutual perspectives between them.
---Practical implications---In practical terms, the main implication of this is that the extent to which the scientific view is given due weight in articles, does not extend so far that there is an actual failure to give due weight or fair mention to significant other views (when they exist), or imply we therefore represent them non-neutrally. If this happens, then there is a NPOV problem, and we need to address it.
No matter how widely respected and correct the scientific view may be, NPOV is still non-negotiable and mandatory for Wikipedia, and if there is a significant minority view, it is given such coverage as may be appropriate according to "due weight". Whether this is a few words, a paragraph, or a section, the following at least should be bourne in mind in the wording:
- Neutrally in weight - neither too much nor too little emphasis and mention.
- Neutrality in description - This signifies how we present a topic or viewpoint in the article. Even the article on flat earth must leave the reader able to understand how flat earthers see it, as well as how and why scientists disagree. Likewise, if there are descriptions of the topic by notable proponents, critics, or commentators, or significant other views, these are given neutral balanced presentation also. We present each view in a way that correctly represents the view or words of its speaker, so to speak. We seek to attribute the words of notable proponents or critics to those people, rather than imply they are "the truth" or "the voice of Wikipedia", so that at the end of the article the reader has a good neutral grasp of the topic, not just of one viewpoint's description of the topic.
- Without disparagement or flattery, whether visible or subtle.
- Without selective representation or citing to make it look deliberately worse than is fair (eg, by choosing weak positive cites, or strong negative ones, or juxtaposing them in a way that deliberately makes the viewpoint seem more flimsy), or deliberately better than is fair (by doing the reverse).
NPOV covers both what is said, and how it is said, since both are important. The sections of WP:NPOV titled "fairness of tone" and "let the facts speak for themselves" cover this more fully.
Last, and briefly, the arbitration case on pseudoscience contains useful clarifications, covering experts and subjects requiring expertize, different types of "alternative view", and related topics in this area. A main principle stated by arbcom was: "NPOV requires fair representation of significant alternatives to scientific orthodoxy. Significant alternatives, in this case, refers to legitimate scientific disagreement, as opposed to pseudoscience."