Dave's ESL Cafe's Student Discussion Forums

[puzzle]

Dear teachers,
Can you tell me when is the article omitted after "act as"?
For example:
1)He acted as secretary to the Board.
2) The chemical acted as a catalyst.
In the first sentence there is no article, but the second one has one, so is there a rule when to use and when to omit?
Thank you!

[pinenut]

1)He acted as secretary to the Board.

'secretary' is a title. There are many other titles such as distric manger, chairman, president, treasurer, director, and so on.

2) The chemical acted as a catalyst.

'a catalyst' is not a title. 'a teacher' is not a title either.