I think that William Butler Yeats is both a realistic and an idealistic poet who conveyed his ideas of history as well as his ideas of what the future portends for humankind to make his significant points to his readers.
In the poem "Sailing to Byzantium", he reveals his thoughts and fears for the future as concerns an aging man...
Consume my heart away; sick with desire
And fastened to a dying animal
In other words, the elderly man desires life and strength and energy to do what he once could do, but this desire is attached to a tired and decaying body and mind. Therefore, Yeats touches on universal realistic themes that often are the facts of advanced age.
In "The Second Coming", Yeats conveys his thoughts concerning the return of Jesus Christ to this earth to establish the Kingdom of God...
Surely some revelation is at hand;
Surely the Second Coming is at hand.
Again, Yeats displays here his idealistic view of the future and insight into his religious beliefs.
In "A Dialogue of Self and Soul", this masterful Irish poet conducts an internal dialogue with himself and here we see his views of life - how we should look at our place on this planet in our particular time.
We must laugh and we must sing,
We are blest by everything,
Everything we look upon is blest.
In the poem "When You Are Old and Grey", Yeats talks about the reality of lost love. He touches on the hurt one feels when love eludes a person. This is a real world view that many experience in life...
Murmur, a little sadly, how Love fled
And paced upon the mountains overhead
And hid his face amid a crowd of stars