幻を追う[maboroshiwoou] to pursue an illusion
幻影[genei] phantom
幻覚[genkaku] hallucination
幻覚剤[genkakuzai] hallucinogen
幻姿[genshi] apparition

幻視[genshi] visual hallucination
幻想[gensou] illusions
幻想劇[gensougeki] non-realistic drama
幻像[genzou] phantom

と考えられる[tokangaerareru] one can think that ...
一考[ikkou] consideration
勘考[kankou] consider
考え[kangae] thinking
考えてみれば[kangaetemireba] if you think about it

考える[kangaeru] to consider
考え込む[kangaekomu] to ponder
考え事[kangaegoto] (deep) thinking
考え出す[kangaedasu] to think out
考え直して[kangaenaoshite] On second thoughts ...