While more can always be said, you might be interested by this Monday Methods post on the topic of declassified documents by /u/restricteddata, which covers how historians get access to and use formerly classified materials.

Alex's Monday Methods post is brilliant. I'd just add a couple of additional cautionary notes on sources.

When teaching, I try to get students to avoid using terms like "reliable/unreliable", "bias/biased", "trustworthy", and so on in relation to sources. These are sometimes used as ways to avoid doing the hard graft of considering sources in a really meaningful, in-depth manner. I always suggest to students that when assessing any primary source, there are three key layers of analysis (of course, this is simply one methodology and is far from the be all and end all):

• Context

• Text

• Subtext

To contextualise, you need to investigate the history that surrounds the source. For example, you might address issues like:

• What is it?

• When was it created?

• Why was it created? [so in relation to your question, why did a hypothetical CIA document come into existence and what purpose was it intended to serve?]

• Who created it? [is it possible to identify which part of the CIA created a particular document? Who within that part contributed? Do we have any sense of tensions between them and other constituencies?]

You should concern yourself with an assessment of the significance of the source by relating it to some more general historical context, movement or event. In this respect, always consider why it is that this particular document has been selected. Your treatment of content should really get into the nuts and bolts of the language, the nuances and allegorical meaning embedded therein (if it’s a written source). In short: what does the source say.

Is it possible to identify the creator of the source? If relevant, what was their geographical/social/institutional location, i.e. what was their background? What were their opinions and to what extent does their identity and personal history shed light upon the nature of the source being considered? Using an example from my own research into concerns about nuclear proliferation amongst Middle Eastern states, certain constituencies within the CIA felt rather burned by the 1979 Iranian Revolution and thence rather over-emphasised the Middle Eastern nuclear issue. In contrast, though, other constituencies within the CIA de-emphasised the threat. I guess the key here is not to think of institutions as monolithic when considering sources, but as made up of individuals and groups with their own agendas.

Further, take into account which issues are consciously raised by the source. Were the issues raised of contemporary relevance, have they remained so, or does a latter-day audience see in the work things never intended by the creator? In short, we need to consider own own biases when examining sources.

You should then turn to the subtext and wider implications of the source and ask yourself the following questions.

• What is implied by the source, but not explicitly stated or presented? What can you understand from ‘reading between the lines’?

• What purpose was this source designed to serve?

• What was the creator trying to achieve? What can you say about the intended audience for the source?

Where a specific audience is not identified in/by the source, what evidence points to the identity of the audience? What comment can you make regarding the synergy between the content of the source and your understanding of the attitude of the audience which was likely to consume this piece? Does it aim to reinforce, or to challenge, prevalent views?

I guess the short version of all of this is that it's crucial to approach sources as sources, not as inherently biased/unbiased, trustworthy/untrustworthy. Context, creator[s], and purpose are all vitally important to consider.

Hope this helps.

Malcolm