Quote mining is a dishonest practice wherein a quote is cut short or taken out of context to change the meaning of the text. This is often used to mislead non-expert audiences into believing wrongly the state of the consensus of expert opinion on a topic. Those who engage in quote mining fail to adhere to the principle of charity, the idea that one must attribute to one's opponent the most favourable (charitable) interpretation of their expressed views. Quote mining can often be a form of arguing from authority as one is not critically engaging with the author one is quoting, but simply relying on them (or, rather, relying on a misquoted version of them) to provide support for some particular view.
Ignoring the following sentence: Darwin
To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
The full context is revealed if one reads on:
Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.
In the passage, Darwin is saying that when faced with the prospect of the eye evolving through natural selection, one is immediately skeptical of such a counterintuitive claim. Left as is, a reader who hasn't read Darwin may be confused and think that Darwin in fact has reached a stumbling block for his theory. But if one reads on, it becomes apparent that the first sentence is setting up a question which Darwin then answers.
Out of the mouth of characters
Fictional texts, and non-fiction texts that contain elements of reported or paraphrased speech can be used for quote mining by taking the words of characters in a text and attributing them to the author.
There is no good or evil; only power, and those too weak to seek it.
This is attributed by some to J. K. Rowling author of the Harry Potter series, and without the context of the book in which it is said, it implies that Rowling is endorsing a form of moral relativism or perhaps Nietzschean "master morality". The quote is from a seemingly likeable character, Quirinus Quirrell, who turns out to be working on the side of evil. Rowling is not Quirrell, nor is Rowling Potter; Dickens is not Scrooge; Mark Twain is not Huckleberry Finn.
Removing the attribution from the text is another way to quote-mine:
There is no god.
The fool has said in his heart, there is no god.
One cannot simply use the first quote and attribute it to the Psalmist, as although it reports the words in the book correctly, it gives an obviously unintended meaning.
Theatrical productions in London's West End have been notorious for quote mining their own reviews. A production may be reviewed very negatively:
The plot could hardly be called exciting and the casting was pantomime-like. I longed for something groundbreaking or even mildly amusing to happen but it never arrived. If you want to see everything that is wrong with contemporary British theatre, this production will not disappoint. That people pay good money to see this dreck brings me to tears.
The advertising outside the theatres will then attribute to the newspaper the single words and phrases that are positive from the review: "groundbreaking", "will not disappoint", "brings me to tears", "exciting" etc.