Idea, Ideal and Ideal

idea = noun meaning a thought, belief, or conception held in the mind, or a general notion or conception formed by generalization:

Greg had a brilliant idea.

ideal = noun meaning something or someone that embodies perfection, or an ultimate object or endeavor:

Greg was the ideal for chefs everywhere.

ideal = adjective meaning embodying an ultimate standard of excellence or perfection, or the best:

John was an ideal candidate.