As far as I know herbs don't mix flavors. You may get a nice combination of smells but flavor won't change. I doubt you could get 3 different herbs in the same 12 inch pot, maybe 2. There just isn't that much room for them to grow.

I have planted a mix of herbs in the same pot--three in a really big pot, about 20" across, I think. Just be sure that the herbs are compatible as to light and water requirements. The only caveat is don't plant mints close together--they make friends with each other and you end up with some strange tasting mints!
I agree with the previous poster in that a 12" pot really is too small for two herbs to thrive. Have you thought about planting one herb per pot, and grouping the pots?

You definitely need to do some homework to find out just how big certain herbs can get when they're fully grown! Beginners are usually very surprised at the results of their research. One mature parsley plant will just about fit a 12" pot. One very stunted basil will be very cramped in a 12" pot. One mint plant will outgrow a 12" pot before you can blink.

In short, a 12" pot is quite a small pot. It is suitable for use when 'potting on' as a plant grows (like children outgrowing shoes and needing the next size up, you won't get them an adult size to begin with). It will accommodate several small seedlings for a short while before they outgrow it and need to be put into individual pots.

You might get away with several coriander plants, or other smaller plants which don't mind a bit of crowding because they are quite short-lived - but consider it a very temporary measure.

Ditto on everything! ;-)

thanks so much for your quick answers
and your help

i will be a good toad and follow your advice :)

mr toad

I have a small, shallow wooden planter that might be slightly larger than 12" but not by much. I like to plan a prostrate rosemary, a thyme and sometimes a third plant depending on what I find at the nursery. Some of the thymes are very slow growing and the rosemary doesn't seem to mind being crowded. I have a lemon verbena in a pot that's about 12" across but deep. It turns into a small shrub during the summer. I like to plant lemon thyme at the base.
I grow several basils but I agree they can get very large so I have a few plants in each pot and do not plant anything with them.
Since I'm in NH with a shorter growing season, that might make a difference. A common garden sage grows fairly quickly and is happy becoming a small shrub in my garden. The variegated sages, however, grow very slowly and sometimes don't survive a New England winter. I would consider planting a variegated sage and a thyme in the same 12" pot but they would need re-potting in the fall.