What is the most common word used for 'idea'?

Question

Pretty sure I've mostly seen idea as アイデア

Does anyone know of other words used for 'idea' and if possible any example sentences and contexts where different words are used?

Answer 1

Use アイディア (or アイデア) when it's replaceable with resolution, suggestion, etc. If you really want to avoid loanwords, you can use "(良い)考え".

What shall we do? Do you have any idea?
何しよう?　何かアイディアある?

An idea is something that solves multiple problems at once. -- Shigeru Miyamoto
アイデアというのは複数の問題を一気に解決するものである -- 宮本茂

Use 概念【がいねん】 (or 考え方) when it's replaceable with concept, way of understanding it, etc. コンセプト may also be a good translation, I think.

The basic idea of Darwin's theory of evolution is that all species of organisms arise and develop through the natural selection ...
ダーウィンの進化論の基本的な考え方/概念/コンセプトは、すべての生物種は自然淘汰を経て発生・発達し…

Use イデア when it refers to the Plato's theory.

According to the theory of Ideas, non-material abstract forms (or ideas), and not the material world of change known to us through sensation, possess the highest and most fundamental kind of reality.
イデア論によれば、我々が感覚を通じて知っている変化する物質世界ではなく、非物質的・抽象的な形式、すなわちイデアが、最も重要かつ基礎的な実在である。

'Idea' in a sentence like this is very difficult to translate using a noun:

Do you have any idea what I am talking about?
私が何を言っているのか分かるか? (or 理解しているか?)