I think Ngugi is right when he sayz the book should be called the river btwn, first take for example honia river btwn the ridges. Isn't the river btwn??
Then we have Waiyaki who is a peace maker trying to join the two groups he is in btwn hence the title the river btwn.
Muthoni a rebellious girl who stands in the way of being a christian n a traditonalist hence in btwn, so i think the title the river btwn is the most appropriate, ther are more other examples on the same.
Ngugi wa Thiong'o chose this title because it is relevant to the book from whatever angle you chose to look at the events in the book.
In the book,there is a river called Honia that divides but at the same time connects the two ridges; Kameno and Makuyu.This river as one can deduce from the many references to its usefulness,is quite important to the community.This may be the superficial source of the title.Looking at it from a deeper perspective, a river is a source of livelihood to the people who live near it whether it is from fishing or any other activity. Therfore the river in this case could symbolise land and culture. This is mainly what brings about conflict between the Europeans and the Africans.Land and culture(mainly Religion) are some of the strongest concepts of an African Community .By bringing a different culture through introduction of Christianity and taking African land,Europeans contaminated the 'purity' of the Gikuyu tribe,just as a river would become polluted by introducing substances to it that don't belong.
Another reason I can think of is that the title fitted the geographical setting of Ngugi's novel.
The river symbolised the rift between the two ridges. Therefore, "The River Between" is appropriate as the book talks about the two ridges' rivalry to one another.
The book is about colonialism more so the struggle kenyans made to unite the people to fight for independence. Kameno and Makuyu were divided. They had different beliefs(kameno were traditionalists while Makuyu were christians), different ways of doing things (Chege lived in a hut built out of mut and cow dung according to the traditional way of building while Joshua had a stone house in accordance to the weastern way of living) and different celebrations- while kameno celebrated circumcision Makuyu celebrated Christmas. the only time these two groups met was at river Honia. This makes the river the uniting factor. Just like the way Waiyaki, Nyambura and Muthoni attempted to unite the two groups. Thefore the title THE RIVER BETWEEN gives the perfect summary of the book. I hope that this was helpfull
Its because according to the text the writer bringes about the river i.e Honia which divides the two ridges.