'vague purpose' is a correct and usable phrase in written English.
It can be used to describe a goal or a task that has not been sufficiently defined or made clear, and is usually used in a negative context. For example: "The project suffered from a lack of direction, with a vague purpose that made it difficult to complete."
A vague purpose like "to tell people about what I've done" doesn't help you design your poster.
"All Hands," a creative mongrel of a show with bursts of inspiration, is about a secret society of vague purpose, filled with smiling members.
When we sit down to a Thanksgiving meal with friends and family, it's easy to overlook the cranberry sauce, that familiar side with a vague purpose.
As Barrie in "Finding Neverland," a handsome-looking film about the writer and his unripe inspirations, Mr. Depp neither soars nor crashes, but moseys forward with vague purpose and actorly restraint.
Of course, as Katharine Murphy has noted, the only reason the prime minister announced this commission was because if he had not done so, enough National party MPs would have crossed the floor next week and voted for one – one that would probably not have had such a vague purpose in its terms of reference.
After surveying the club, which was so sleazy its wallpaper was the same design as Robin Thicke's suit, I found out that the vague purpose of the night was to recreate Tinder IRL.
The function Purpose also recognizes the vague purposes as unequal state.
The agent was there to ask Rosenberger to kindly withhold posting the information or else for vague purposes of "national security" following the Sept. 11 terrorist attack.
Deal contracts are often left vague on purpose.
When candidates leave details unspecified, they're being vague on purpose, either to put off tough legislative choices, tough political choices or both.
"When people ask him the question of the day after" -- meaning after Mr. Arafat is gone -- "he is always very vague on purpose".
