Full Idea
If a man does not respond to a greeting, if he was unaware that he was addressed then his failure to respond may be a mere omission. But if he intended to snub the man, then he could be said to have 'committed the omission'.
Gist of Idea
There are mere omissions (through ignorance, perhaps), and people can 'commit an omission'
Source
Roderick Chisholm (Person and Object [1976], 2.6)
Book Reference
Chisholm,Roderick: 'Person and Object' [Open Court 1976], p.73
A Reaction
Chisholm has an extensive knowledge of Catholic theology. These neat divisions are subject to vagueness and a continuum of cases in real life.