A prohibition is a command not to do something. Neither prohibitions nor precepts need to have imperative sentences for their expression. Grammatically indicative sentences can communicate prohibitions (“Spitting is forbidden.”) Imperatives are, however, a typical form of expression for both. We can issue a warning and in a broad sense a prohibition (“Don’t go too close to the edge.”) There’s a narrow sense in which warning and prohibiting are different, though, and Hare suggests the difference resides in the presence (in prohibiting) or absence (in warning) of an internal reference in the nature of the speech act to the authority of the speaker, and to some form of condemnation envisaged for failing to comply.
Examples of prohibitive commands will be like examples of preceptive commands, except in the negative. But there will often be a positive command going along with the prohibition. In experience, sometimes the negative has the focus, sometimes the positive; perhaps with God’s commands it’s more often the negative. Socrates reported that his voice only told him what not to do. But there may be positive implications of prohibitions. The Heidelberg Catechism, to take just one example, acknowledges that the second table of the Ten Commandments consists almost entirely of prohibitions, but it insists that there are positive correlates to all the negatives, and that they are equally enjoined.
Examples of prohibition are easy to find, but the attribution to a divine source will often seem indicated only when the prohibition is unexpected or unusually vivid. The restriction comes from our own natural caution, not wanting to ascribe to God what could be just our own mental processing. But as with precepts, there’s no need to posit that we always perceive the divine source, or that God always uses extraordinary means of revelation, so that God’s prohibitions may in fact be much more frequent than we are inclined to credit.
Here is an example of a prohibition. A person has found his sibling difficult, and decides finally to send her a book, which he thinks will do her good. At the time of sending it, he hears a still small voice in his head telling him that this is a bad idea. But he ignores it, and puts the book in the mail. Somehow, the book gets lost and is never delivered. At this point, the voice in his head gets more insistent, telling him to leave well enough alone. But he’s stubborn, and buys another copy of the book, and sends it off. This time, the book is delivered, and it’s a disaster. He and his sibling have a row, after she has read the book, which very nearly destroys their relationship. He realizes that he had in fact known all along that God was telling him not to send it.
Image: By Fritz von Uhde - http://www.neumeister.com, Public Domain, https://commons.wikimedia.org/w/index.php?curid=47654827