This is a difficult question to answer because I am not sure which kind of encyclopedia you are referring to or what you mean by "primary". Technically, encyclopedias are not primary sources or even secondary sources. Therefore, encyclopedias are a poor source of primary information because they are unreliable. While they may have information about a chosen topic that is supposedly unbiased and factual, because they are not actual sources of information for anything other than a quick summary of something, they are unreliable. In terms of Wikipedia, they are incredibly unreliable because anyone can edit the information on the topic. In terms of old hard copies of encyclopedias, they often do not have current information, but you can always look at the newest editions. Encyclopedias are notoriously vague because they are only capable of containing a small amount of information on a much larger issue, most encyclopedias are written incredibly well.
