He grew interested in philosophical mysticism, as well as universalism, addressing these subjects in his works such as The Perennial Philosophy, which illustrates commonalities between Western and Eastern mysticism, and The Doors of Perception, which interprets his own psychedelic experience with mescaline.
hiː ɡɹˈuː ˈɪntɹɛstᵻd ɪn fˌɪləsˈɑːfɪkəl mˈɪstɪsˌɪzəm, æz wˈɛl æz jˌuːnɪvˈɜːsəlˌɪzəm, ɐdɹˈɛsɪŋ ðiːz sˈʌbdʒɛkts ɪn hɪz wˈɜːks sˈʌtʃ ɐz ðə pəɹˈɛnɪəl fɪlˈɑːsəfi, wˌɪtʃ ˈɪləstɹˌeɪts kˌɑːmənˈælᵻɾiz bᵻtwˌiːn wˈɛstɚn ænd ˈiːstɚn mˈɪstɪsˌɪzəm, ænd ðə dˈoːɹz ʌv pɚsˈɛpʃən, wˌɪtʃ ɪntˈɜːpɹɪts hɪz ˈoʊn sˌaɪkɪdˈɛlɪk ɛkspˈiəɹɪəns wɪð mˈɛskəlˌaɪn.