He began his career as a candidate for the ministry but turned to philosophy as his major academic interest after graduating, though he continued to preach throughout his life. He preached throughout Wales and gave addresses several times at meetings of the (CM) Association . His preaching was characterised by unusual passion which led many to refer to him as a prophet.

In his philosophical work he concentrated on three problems — the nature of the self, the nature of perception, the nature of universals. Of these the most important for him was the question of the nature of the self, and this was the subject of his first and of his last contributions to Efrydiau Athronyddol . Later in his career he was influenced by the ideas of Tillich , Wittgenstein and Simone Weil . During this period he delivered his television address Yr Argyfwng Gwacter Ysbryd (‘the crisis of meaninglessness’), later published as a pamphlet which gave a new phrase to the Welsh language.

After moving to Swansea and seeing the decline of Welsh in the south Wales valleys his interest turned to the condition of Wales ; and after his return from America where he had become aware of the lack of roots in the 1960s , he became increasingly concerned about the crisis of Wales and of Welsh . During his last years this was his main concern. He strongly opposed the 1969 Investiture and resigned as one of the editors of Y Drysorfa and as a member of the Gorsedd of Bards . He wrote Prydeindod (‘Britishness’) at this time and delivered several address to the Welsh Language Society . During the final months of his illness he prepared two books for the press, Gwaedd yng Nghymru and Ac Onide , both of which were published after his death. He d. 3 June 1970 at his home in Swansea and was buried in Pwllheli .

He published a number of books and pamphlets: Yr Argyfwng Gwacter Ystyr ( 1964 ); Prydeindod ( 1966 ); Arwyddion yr Eiriolaeth (from Yr Ymofynnydd ); Cristnogaeth a Chenedlaetholdeb ; ‘ Gweithredu Anghyfreithlon ’ in Areithiau Eisteddfod Aberafan ; Ni fyn y taeog mo'i ryddhau ( 1968 ); A rhaid i'r iaith ein gwahanu? ( 1967 ); Yr ewyllys i barhau ( 1969 ); Gwaedd yng Nghymru ( 1970 ); Ac Onide ( 1970 ); Welsh articles on philosophy and religion in Y Drysorfa , 1933 , 1943 , 1949 ; Credaf , 1944 ; Taliesin , 1967 ; Efrydiau Athronyddol , 1938 , 1939 , 1947 , 1950 , 1951 , 1957 , 1961 , 1969 ; Diwinyddiaeth , 1969 ; Y Drysorfa 1956 ; Saith ysgrif ar grefydd (ed. Dewi Z. Phillips ), 1967 ; in English , Religion as true myth (inaugural lecture Univ. Coll. of Swansea , ( 1953 ); articles in Mind , 1948 , 1950 , 1954 ; Philosophical Review , 1949 , 1951 ; Philosophy , 1950 ; Philosophical Studies , 1950 ; Philosophical Quarterly , 1951 ; Aristotelian Society Symposium Suppl. , 30 ( 1956 ), Proc. , 49 ( 1958-59 ); Presidential Address , 1967 ; Analysis , 1950 ; Congregational Quarterly , 1950 ; Sophia , 1970 ; and in Religion and Understanding (ed. Dewi Z. Phillips , 1967 ).