I have had an idea [closed]

Solution 1:

The present perfect continuous (even though it is, grammatically, the continuous form) refers to a series of interrupted occurrences. If you have had the same idea more or less constantly in an unaltered form in your mind for a period of time you use the simple past tense "I have had this idea for some time". If, however, you have had multiple ideas on the same theme you use the present continuous "I have been having these ideas for some time now".

A clearer example, perhaps, is the pair of sentences:

"I have had this migraine for 24 hours now."

(the migraine stared 24 hours ago and has never gone away)

as opposed to

"I have been having migraines since I was a teenager."

(not the same migraine in all that time, obviously, but suffering from the condition for years).