Pseudepigrapha in the NT letters

The word refers to writings ascribed to the name of a certain author, but actually written by someone else – under a pseudonym. Books that are falsely (pseud) named (onoma). In the ancient world this may have been done in order to deceive, promote certain teachings without the linking oneself to them, or promote the ideas of a deceased teacher by compiling them under their name. Around the middle of the second century Christians works such as the famous “gospel of Thomas” appeared in this way, claiming to be by the apostles. Where scholars of the New Testament find significant differences in vocab, ideas and structure between certain letters purported to be by the same authors, some therefore argue that the more novel seeming letters fall into this category and are not actually written by the apostle they claim to be written by. NT letters that people question are Ephesians, Colossians, 2 Thessalonians, 1 and 2 Timothy, Titus, 1 and 2 Peter. Some suggest there were “schools” of those who studied certain apostles, and that it was quite acceptable for them to write these letters in their name.
            A number of responses can be given: (1) There is no evidence at all of “schools” operating in this way, nor of the early church “fathers” (leaders) accepting the practice. (2) On the contrary, the fathers were extremely concerned with whether or not a book was written by an apostle, as only those linked to them were considered inspired scripture. They therefore firmly condemned any who sought to write in the name of an apostle. The Roman "Muratorian" fragment from 190AD rejects two letters it says were "forged" in Paul's name, and around the same time Serapion of Antioch notes writings that "falsely bear" the name of apostles, rejecting a gospel said to be by Peter. (3) The NT letters claim apostleship in order for their teachings to be read and received with apostolic authority, often appealing to the relationship with apostle had with the readers. This means the entire point of the letter would be undermined if written by another, making a well meaning compilation of the apostle’s ideas in this form a waste of time. (4) In 2 Thessalonians the author actually condemns pseudonymity (2v1-2, 3v17) – a bizarre act if not the apostle Paul himself. The writer of 2 Peter likewise contrasts those who make things up with his own eyewitness testimony (1v16). (5) It is clear that the apostles did sometimes use scribes (amanuenses) as Paul mentions in Romans 16v22, contrasting when he writes with his “own hand” (Gal 6v11). Peter may be implying the same in 1 Peter 5v12. This would be a ready explanation for why the vocab, structure and even shaping of ideas might be different between letters sourced in the same apostle. (6) Differences might also be explained simply by the passage of time in which such things inevitably develop. (7) The claims the letters make mean that any pseudonymity is blatant deception rather than well meaning literary style. And it is unthinkable in the light of the high value of truth and honesty within the early church that those so committed as to be able to write such a letter would also be so ready to deceive.
For further reading see Carson, D. A. (2000). Pseudonymity and Pseudepigraphy. In Dictionary of New Testament background: a compendium of contemporary biblical scholarship (electronic ed., p. 857). Downers Grove, IL: InterVarsity Press.