Receiving credit by way of acknowledgment rather than authorship indicates that the person or organization did not have a direct hand in producing the work in question, but may have contributed funding, criticism, or encouragement to the author(s). Various schemes exist for classifying acknowledgments; Giles & Councill (2004) give the following six categories:
Apart from citation, which is not usually considered to be an acknowledgment, acknowledgment of conceptual support is widely considered to be the most important for identifying intellectual debt. Some acknowledgments of financial support, on the other hand, may simply be legal formalities imposed by the granting institution.