This book is his reaction against the violent century which he was born into and which was born into him. He speaks against issues including such things as the true nature of the monastic relationship with the world (he calls "separation from the world" an illusion); unity/ecumenism; war & violence; false "truths" (particularly what he calls the American myth); technology versus nature, etc.
He calls himself a "bystander" relating to his aloofness as a monk. He calls himself "guilty" in relation to not living up to his responsibility for the outside world. As a monk, he calls himself a contemplative activist. As a collection of "conjectures," it is a compilation of thoughts or pensees grouped together loosely, only slightly tied together by five section titles. Because of this format it is not the easiest thing to read; it is helpful to read topically (a good guide for this can be found in Something of a Rebel by William Shannon). But I would say the experience is worth it. The book is deeply moving and convicting. Merton stands out as an authoritative voice on how Christians, all people in fact, should be aware of the world around them, while they also should not neglect the contemplative life that feeds their love for that world.
There is a short observation Merton gives us in his Conjectures as he witnesses the way of the world around him:"This morning, before Prime, in the early morning sky, three antiquated monoplanes flew over the monastery with much noise followed by a great heron." (15)
Commenting on this thought, Thomas Moore writes in his introduction to Conjectures: "Many antiquated machines have come and gone in the time since Merton wrote these lines, an explosion of technology giving the illusion of progress, while Merton himself continues to fly, pulling up the rear, a great silent heron reminding us that the noisy are not necessarily the knowledgeable." (v)
Some of this book is quaint and linked too much to the time of its writing. Merton's writes nearly vitriolic reflection on communism but does not foresee the rise of liberation theology in his own church. However, there are many other portions where the author moves beyond the context of his time. Merton's reflections on race-relations, for example, are unusually compassionate for a writer of his time, for he believes that African-Americans are blessed by God, who was bringing them in freedom from exile, slavery, and oppression like the Hebrews.
When I was younger and full of idealistic fire, having just left the Navy as a conscientious objector, I couldn't understand Merton. Here was a man who was full of zeal for the gospel, but who turned away from the community for a hermitage in rural Kentucky. From CONJECTURES, however, I can better appreciate this writer. Though he was alone, he has made a considerable contribution to society through books like these. Merton essentially wishes to make people live more authentically, to always be more conscious of Christ's social teaching and reject the false values of the world. Merton may have been a recluse, but if more people out and about in society read his writings, then the world would be a better place. For example, though Merton is not one to overtly recommend political engagement, he often calls the American reader to consider that his nation has strayed from the values on which they were founded and needs righting.
If you have never read Merton before, I'd recommend starting with THE SEVEN-STOREY MOUNTAIN, the story of his youth, conversion, and entry to a Trappist monastery, a book which occasionally rises to true greatness and might be a modern-day CONFESSIONS of Saint Augustine (well, almost). CONJECTURES is an excellent book for those interested in Merton who want to know better his social ideas.