I was listening to a language learning CD the other day. After every passage, there were some exercises, preceded by the instruction ‘please answer the questions based on the text’.
The intended meaning is: ‘please answer the question and base your answers on the text’. But read literally, it seems to be saying: please answer the questions. By the way, the questions are based on the text’.
Of course, it’s clear what the instruction meant, but the wording isn’t very elegant.
A wider problem
This is just one example of a wider problem in how people use the phrase ‘based on’. I first became of the problem through working with an editor who often used to complain about it. The issue arises because based is an adjective (or sometimes an adjectival participle). But people often use based on [+ noun phrase] as an adverbial not integrated in the main structure of the clause.
People sometimes describe this sort of usage as ‘absolute’—I think because Latin has a construction often called the ablative absolute. In that construction, a noun in the ablative case is not integrated in the clause.
So, that editor used to accept based on only when a preceding noun phrase refers to an item that is based on something referred to by the following noun phrase. So, he would accept ‘your answer is based on the text’. But he wouldn’t accept ‘please answer based on the text’. In cases like that, he would replace based on with on the basis of. So, ‘please answer on the basis of the text’. Or ‘please answer the questions on the basis of the text’.
I found my editorial former colleague’s analysis persuasive. So, for the last 15 to 20 years, I have generally followed his practice of replacing based on with on the basis of when the phrase is being used in an absolute sense as an adverbial, rather than as a prepositional phrase. Although using based on in such cases rarely causes ambiguity or a misunderstanding, it does make writing inelegant.