Top 19+ Mind-Bending Books In Order (2023) For Readers Like To Wonder
The following list includes the most mind-bending books of all time, known for their thought-provoking, imaginative, and challenging content. These books often explore unconventional ideas, make readers question reality, and push the boundaries of traditional storytelling.
The list is in reverse-chronological order, starting with the latest releases.
What Are the Most Mind-Bending Books of All Time?
Conjunction, by A.D. Zoltan & Steven N. Nagy (2022)
A spiritual science fiction that explores the real nature of psyche, puts our whole existence in context, and what the real nature of the universe might be like.
Conjunction is a truly intriguing and thought-provoking work. The authors' passion for exploring spirituality and the idea of an utopian society shines throughout the book, as they delve into complex philosophical concepts and paradoxes.
What particularly struck me was the creation of the Füzenis, an advanced alien civilization that helps the human protagonist to understand spirituality on a deeper level. This unique approach to the topic makes the book stand out and offers a fresh perspective on the meaning of life and the ‘afterlife'.
Moreover, the authors' emphasis on character development and connections between them adds a level of depth and engagement to the story.
It was interesting to understand the ‘Erin scale' that measures a civilization's level of consciousness. The authors invite readers to reflect on the potential of humanity to grow beyond the limitations of our current understanding.
The fusion of philosophy, spirituality, and world-building within the book makes Conjunction a captivating and truly mind-bending read that leaves a lasting impression.
Dark Matter, by Blake Crouch (2016)
Dark Matter was an electrifying and mind-bending reading experience that had me hooked from the very start. The novel plunges into the realms of quantum mechanics and the multiverse, following the protagonist, Jason Dessen, as he navigates a seemingly alternate version of his life. Crouch's fast-paced, suspenseful storytelling and his seamless integration of complex scientific concepts into the narrative made Dark Matter a thrilling and thought-provoking read.
One potential criticism of Dark Matter could be its heavy reliance on scientific concepts and jargon, which might be challenging for some readers to grasp. However, Crouch's skillful exposition and deft handling of the subject matter ensure that even readers without a background in quantum mechanics can enjoy the novel's twists and turns. Moreover, the novel's exploration of themes such as love, family, and the consequences of our choices lend it emotional depth and resonance that goes beyond mere intellectual exercise.
Ultimately, Dark Matter is a gripping and thought-provoking novel that pushes the boundaries of conventional storytelling and leaves the reader pondering the mysteries of the universe and the complexities of the human experience.
Annihilation, by Jeff VanderMeer (2014)
The novel is filled with suspense, psychological intrigue, and a sense of otherworldliness that keeps readers questioning reality and the nature of human existence.
Upon delving into Annihilation, I was immediately struck by the eerie, otherworldly atmosphere that pervades the pages of this enigmatic novel. I eagerly embraced the novel's unconventional narrative style and imaginative premise, as I joined a team of four unnamed women on their expedition into the mysterious Area X. VanderMeer's evocative prose and masterful world-building transported me to a realm that was both hauntingly beautiful and deeply unsettling, leaving me on the edge of my seat as I attempted to unravel the secrets of this enigmatic landscape alongside the novel's intrepid protagonists.
Of course, Annihilation is not without its challenges for the discerning reader. VanderMeer's penchant for ambiguity and his resistance to providing clear-cut answers may frustrate those who prefer a more straightforward narrative.
However, for readers who relish the opportunity to immerse themselves in the unknown and grapple with thought-provoking questions about the nature of reality, identity, and the limits of human understanding, Annihilation is a true gem.
I found myself captivated by VanderMeer's unique blend of psychological intrigue, suspense, and richly layered storytelling.
The Bone Clocks, by David Mitchell (2014)
This ambitious, genre-defying novel is a sprawling, interconnected narrative that weaves together the lives of its diverse characters across time and space.
With its genre-defying narrative, the novel masterfully weaves together the lives of its diverse cast of characters across time and space, spanning from the 1980s to the 2040s. Mitchell's incredible storytelling ability, combined with his exploration of themes such as interconnectedness, mortality, and the power of storytelling itself, made The Bone Clocks a thought-provoking and captivating read. As I navigated the novel's intricate plotlines and delved into the richly detailed worlds Mitchell created, I found myself marveling at the sheer scope and ambition of this literary masterpiece.
The novel's complex structure and fantastical elements could be overwhelming or disorienting for some readers. While the book's central narrative is deeply interconnected, the individual stories within it may at times feel disjointed, requiring the reader to piece together the larger picture from fragments of each character's life.
Yet, for those who embrace Mitchell's ambitious storytelling and his ability to blur the lines between genres, The Bone Clocks offers a truly rewarding reading experience.
The novel left me with a profound appreciation for the power of literature to transcend time, space, and our own limited perspectives, reminding us of the fundamental interconnectedness of all things.
The Road, by Cormac McCarthy (2006)
A bleak and haunting novel set in a post-apocalyptic world, exploring themes of survival, morality, and the human spirit.
The Road is a haunting and gripping novel that left an indelible impression on me.
Set in a post-apocalyptic world, the story follows a father and his young son as they journey through a desolate landscape, struggling to survive and retain their humanity in the face of unimaginable hardship. McCarthy's sparse, poetic prose and his unflinching portrayal of the bleak and unforgiving environment created an atmosphere that was at once starkly beautiful and deeply unsettling.
The protagonists on their perilous journey, I felt myself profoundly moved by their bond and their determination to persevere despite the seemingly insurmountable obstacles they faced.
What truly resonated with me about The Road was its exploration of the resilience of the human spirit and the enduring power of love in even the darkest of circumstances. McCarthy's masterful storytelling and his ability to evoke the depths of human emotion without resorting to sentimentality provided a reading experience that was both intellectually challenging and deeply moving.
While the relentless bleakness of the novel's setting and subject matter may be difficult for some readers to bear, I found that the moments of tenderness and hope amidst the darkness served as a powerful testament to the capacity for compassion and empathy that lies at the core of our humanity.
House of Leaves, by Mark Z. Danielewski (2000)
A complex and layered novel that experiments with typography and narrative structure, exploring themes of love, loss, and fear.
Upon delving into House of Leaves, I was immediately captivated by its unique and innovative format. The labyrinthine structure, replete with footnotes, multiple narrators, and a blend of different storytelling styles, made reading the book an immersive and exhilarating experience. Each turn of the page seemed to hold a new surprise, as the experimental layout compelled me to engage with the text in a way that I had never encountered before. Danielewski's ability to manipulate the very form of the book itself to evoke a sense of disorientation and claustrophobia mirrored the eerie, shifting nature of the titular house, further drawing me into the chilling tale.
The story itself, a complex web of narratives exploring themes of love, loss, and the unknown, only served to heighten my appreciation for House of Leaves. I was enthralled by the enigmatic tale of the Navidson family and their impossible, ever-changing house, as well as the parallel story of Johnny Truant, whose own descent into madness mirrored the dark, twisting corridors of the house.
Danielewski's skillful interweaving of these seemingly disparate narratives led me to ponder the nature of reality, the fragility of human relationships, and our own innate fears of the unknown.
Infinite Jest, by David Foster Wallace (1996)
A sprawling and complex novel that challenges conventional storytelling, delving into themes of addiction, entertainment, and the search for meaning.
Infinite Jest was a literary journey that challenged and captivated me in equal measure. From the moment I began reading, I was struck by Wallace's unique and intricate writing style, which masterfully wove together a vast array of storylines, characters, and themes. The novel's scope was both ambitious and daunting, but I found myself drawn into the complex world of addiction, entertainment, and the search for meaning. The sheer density of the text, with its extensive footnotes and numerous subplots, demanded my full attention and rewarded me with a reading experience that was as intellectually stimulating as it was emotionally resonant.
What made me truly appreciate this book was the way it delved deep into the human psyche, exploring the lengths to which we go in our pursuit of happiness and the dangers that lie in unchecked consumption. Wallace's keen observations on modern life, combined with his dark humor and profound insights, resonated with me on a personal level. As I navigated the labyrinthine narrative, I found myself not only entertained but also profoundly affected by the characters and their struggles.
The novel's unflinching examination of addiction, loneliness, and the human condition left me with a new understanding of the complexities of life in the modern era. In the end, Infinite Jest was a transformative experience that expanded my perspective on the world and the myriad ways in which we seek connection and meaning in our lives.
The Wind-Up Bird Chronicle, by Haruki Murakami (1994)
A surreal and metaphysical novel that explores themes of fate, identity, and the subconscious.
The novel follows the seemingly ordinary life of Toru Okada, who is drawn into a surreal and mysterious world as he searches for his missing wife and cat. Murakami's signature blend of magical realism, richly drawn characters, and evocative prose created a narrative that was both dreamlike and grounded in the everyday experiences of love, loss, and self-discovery.
As I followed Toru's journey into the unknown, I found myself enthralled by the novel's intricate web of interwoven stories and the compelling exploration of the human psyche, history, and the nature of reality.
What I truly appreciated about this mind-bending story was its ability to challenge my preconceptions and force me to confront the often inexplicable aspects of life and human existence. Murakami's skillful storytelling and his penchant for blending the fantastical with the mundane provided a deeply engaging and thought-provoking reading experience that left me pondering the novel's themes and ideas long after I had turned the final page.
Some readers might find the narrative's loose ends and ambiguity frustrating, but I found that the novel's refusal to provide clear answers or resolution only heightened its allure, encouraging me to embrace uncertainty and the power of imagination.
The Wind-Up Bird Chronicle was not only an enthralling work of fiction but also a profound meditation on the complexities of life, love, and the human spirit.
Blood Meridian, by Cormac McCarthy (1985)
A dark and violent novel that explores the brutality of humanity, set in the American West during the 19th century.
This book has a stark, brutal portrayal of the American West and its exploration of the dark undercurrents of human nature. From the outset, I was struck by McCarthy's evocative, often poetic prose, which painted a vivid picture of the unforgiving landscape and the violent, morally ambiguous characters that inhabited it.
The story, centered around the enigmatic Judge Holden and the young protagonist known as “the kid,” was a harrowing journey into the heart of darkness, as I bore witness to the horrific acts committed in the name of survival and conquest. McCarthy's unflinching exploration of violence, power, and the human capacity for evil provided a haunting and thought-provoking reading experience that left an indelible mark on my psyche.
As I delved deeper into Blood Meridian, I found myself grappling with the novel's complex themes and the unsettling questions it raised about the nature of humanity, morality, and the inevitability of violence. While the relentless brutality of the narrative could at times be difficult to stomach, I came to appreciate the importance of confronting these aspects of our history and acknowledging the darkness that lies within us all. McCarthy's refusal to provide easy answers or redemption for his characters only served to heighten the sense of unease and challenge my own beliefs and assumptions.
Blood Meridian was not only a masterful work of literature but also a profound meditation on the human condition, pushing me to reflect on the depths of our capacity for both good and evil.
The Hitchhiker's Guide to the Galaxy, by Douglas Adams (1979)
A comedic science fiction series that explores themes of absurdity, the nonsense of life, and the nature of the universe.
I reveled in Adams' irreverent take on science fiction, as he whisked me away on an interstellar adventure alongside the endearingly hapless Arthur Dent and his extraterrestrial guide, Ford Prefect. Adams' witty, satirical prose and his uncanny ability to find humor in the most unexpected places transformed this cosmic romp into a laugh-out-loud journey that had me questioning the absurdity of our own existence and the nature of the universe itself.
Admittedly, The Hitchhiker's Guide to the Galaxy may not be everyone's cup of tea, as its distinctive blend of satire, absurdism, and biting wit veers away from conventional storytelling. However, for those with an appetite for the offbeat, Adams' novel is a true delight that serves up a hearty helping of tongue-in-cheek commentary on life, the universe, and everything in between.
In a world where science fiction can sometimes take itself too seriously, The Hitchhiker's Guide to the Galaxy is a breath of fresh intergalactic air that reminds us of the importance of embracing the inherent silliness of our very existence. So, grab your towel, don your electronic thumb, and prepare to hitch a ride on this uproarious, thought-provoking adventure through the cosmos!
Gravity's Rainbow, by Thomas Pynchon (1973)
A complex and dense novel set during World War II, exploring themes of paranoia, technology, and the nature of humanity.
Gravity's Rainbow captivated me with its incredible depth, complexity, and scope. Set during the closing months of World War II, the novel weaves together an intricate web of characters, storylines, and themes, exploring the dark underbelly of technology, paranoia, and the human psyche. I was immediately drawn to Pynchon's dense and erudite prose, which required my full attention and rewarded me with a reading experience that was as challenging as it was exhilarating.
The sprawling narrative, populated by a vast array of eccentric characters and punctuated by moments of absurd humor and profound insight, made Gravity's Rainbow a truly unforgettable journey.
What I loved most about Gravity's Rainbow was its ability to push the boundaries of what a novel can be. Pynchon's fearless exploration of topics such as power, control, and the role of technology in our lives, as well as his willingness to delve into the most obscure corners of human experience, made the book an intellectual and emotional tour de force.
As I navigated the labyrinthine plot, I found myself constantly questioning my own assumptions and beliefs, ultimately gaining a greater understanding of the complexities of the modern world.
Ubik, by Philip K. Dick (1969)
A science fiction novel that explores themes of reality, identity, and corporate power in a future dystopian society.
The novel's intriguing blend of science fiction, mystery, and metaphysical exploration captivated me, as I followed protagonist Joe Chip and his colleagues in their struggle to decipher the nature of their reality after a disastrous mission.
Philip Dick's signature writing style, with its combination of dark humor, philosophical inquiry, and imaginative storytelling, made for an exhilarating and thought-provoking reading experience that constantly challenged my perceptions of reality and the nature of existence.
What I truly appreciated about Ubik was its ability to address complex themes such as the nature of reality, the passage of time, and the boundaries of human consciousness through an engaging and suspenseful narrative.
As I navigated the twists and turns of the plot, I was constantly questioning the nature of the reality presented in the novel, and by extension, the nature of our own existence. The author's masterful storytelling and his talent for blending elements of mystery, suspense, and metaphysical inquiry resulted in a novel that was not only entertaining but also deeply thought-provoking.
Ubik left me with a greater appreciation for the power of speculative fiction to challenge our understanding of the world and to explore the deepest questions of human existence.
Slaughterhouse-Five, by Kurt Vonnegut (1969)
A satirical novel that addresses themes of war, time, and the human condition through a nonlinear narrative.
This mind-bending book was a reading experience unlike any other I've encountered. I was instantly drawn to the book's unconventional narrative structure and Vonnegut's signature blend of satire, humor, and tragedy. The protagonist, Billy Pilgrim, with his unique perspective on time and his experiences as a prisoner of war during the bombing of Dresden, captivated my imagination.
The author's use of science fiction elements, like Billy's encounters with the Tralfamadorians, served as an inventive way to explore the human condition and the absurdity of war. His dark humor and poignant reflections on the nature of life, death, and time provided moments of both laughter and contemplation.
What truly made me appreciate Slaughterhouse-Five was Vonnegut's ability to address the trauma and devastation of war through the lens of his own experiences while maintaining an accessible and engaging narrative. The novel's central theme, the idea that we are powerless to change the course of our lives, made me ponder the concept of free will and the impact of our choices.
Vonnegut's masterful storytelling and unconventional approach to narrating Billy's life story struck a perfect balance between entertaining and thought-provoking, leaving me with a newfound perspective on the complexities of the human experience. In the end, Slaughterhouse-Five was not only an unforgettable read, but it also served as a powerful reminder of the resilience of the human spirit in the face of adversity.
The Master and Margarita, by Mikhail Bulgakov (1967)
A satirical and fantastical novel that intertwines themes of religion, politics, and art in Soviet Russia. I would say that this image what the author shows to the readers is more real than ever nowadays.
Set in Moscow during the 1930s and interwoven with a retelling of the biblical story of Pontius Pilate, the book explores the interplay between good and evil, love and despair, and art and censorship. I was immediately drawn to the colorful cast of characters, ranging from the mysterious Professor Woland and his motley crew to the tormented Master and the devoted Margarita.
Bulgakov's masterful storytelling, rich with wit and vivid descriptions, created a world that was both fantastical and grounded in the harsh realities of Soviet life.
What truly made me appreciate The Master and Margarita was its ability to address complex and profound themes with humor and grace. Bulgakov's exploration of the power of art, the nature of human morality, and the importance of personal integrity resonated with me deeply.
The novel's various storylines and their intricate connections left me pondering the complexities of life, love, and the human spirit. Moreover, Bulgakov's own struggle with censorship and the suppression of his work imbued the novel with an added layer of poignancy, highlighting the importance of artistic freedom and the value of perseverance in the face of adversity.
One Hundred Years of Solitude, by Gabriel García Márquez (1967)
A multigenerational saga that blends magical realism with historical events, exploring the cyclical nature of time and the human experience.
From the moment I began reading this book, I was instantly captivated by the vivid, magical world he created. The sprawling saga of the Buendía family, set against the backdrop of the mythical town of Macondo, was a mesmerizing tapestry of love, loss, and the relentless passage of time.
Márquez's masterful storytelling, infused with elements of magical realism, transported me to a realm where the extraordinary became commonplace, and the boundaries between reality and fantasy blurred. The richly-drawn characters and their intertwined destinies enthralled me, making it impossible to put the book down.
What truly made me appreciate One Hundred Years of Solitude was its exploration of timeless themes such as the cyclical nature of history, the complexity of human relationships, and the search for identity. As I followed the multi-generational narrative, I found myself reflecting on the ways in which our personal histories and those of our ancestors shape our lives and the world around us.
Márquez's evocative prose and his ability to weave together seemingly disparate threads into a cohesive and emotionally resonant whole left a deep impact on me. In the end, One Hundred Years of Solitude was not only a spellbinding and immersive reading experience, but it also provided me with a new perspective on the interconnectedness of our lives and the enduring power of storytelling.
Catch-22, by Joseph Heller (1961)
A satirical novel that explores the absurdity and futility of war, bureaucracy, and human suffering.
Joseph Heller's Catch-22 was a novel that immediately captured my attention with its biting satire, dark humor, and poignant portrayal of the absurdity of war. Following the misadventures of Captain John Yossarian, a bombardier stationed in Italy during World War II, I was drawn into a world where bureaucracy and illogical rules reign supreme, and where self-preservation often clashes with duty.
The author's unique narrative style, non-linear storytelling, and larger-than-life characters, like the opportunistic Milo Minderbinder, made for an engaging and thought-provoking reading experience that constantly kept me on my toes.
What I truly appreciated about Catch-22 was its ability to shed light on the insanity of war and the human condition through its sharp wit and unrelenting absurdity. As I followed Yossarian's struggle to navigate the treacherous landscape of military regulations and contradictory logic, I couldn't help but reflect on the inherent contradictions present in our own lives and the ways in which we cope with them.
Heller's masterful storytelling and his gift for blending humor with tragedy resulted in a novel that was not only entertaining but also deeply moving.
This book left me with a greater appreciation for the power of satire to reveal the follies of human nature and the need to question the systems that govern our lives.
Naked Lunch, by William S. Burroughs (1959)
A nonlinear and experimental novel that delves into themes of addiction, control, and the human condition.
William S. Burroughs' work was an enthralling and deeply challenging reading experience that pushed the boundaries of conventional storytelling. The novel's fragmented, nonlinear structure and its exploration of taboo subjects and the darker aspects of human nature provided a stark departure from traditional narrative forms.
Burroughs' raw, visceral prose and his use of satire and dark humor drew me into a hallucinatory world, populated by a host of grotesque characters and disturbing imagery. As I navigated the disjointed narrative, I found myself confronted with the novel's unflinching examination of addiction, power, and the human psyche.
While Naked Lunch‘s unconventional form and content could at times be disorienting and even shocking, I came to appreciate the importance of challenging literary norms and pushing the limits of artistic expression. The novel's unique blend of satire, social commentary, and surrealism forced me to confront my own preconceptions and prejudices, ultimately broadening my understanding of the complexities of human experience. However, some readers might find the graphic and explicit nature of the novel off-putting or difficult to digest.
Nevertheless, Naked Lunch remains a groundbreaking work of literature that continues to provoke discussion and debate, serving as a testament to the power of art to challenge, inspire, and transform our understanding of the world around us.
1984, by George Orwell (1949)
A dystopian novel that presents a chilling vision of a totalitarian society and explores themes of surveillance, propaganda, and manipulation.
As a fan of classic literature, I was instantly drawn to George Orwell's 1984. The dystopian narrative, with its bleak portrayal of a totalitarian society, captivated me from the very beginning. Orwell's masterful storytelling transported me to the grim world of Oceania, where I found myself entangled in the life of the protagonist, Winston Smith. I could not help but empathize with his yearning for freedom and truth in a society where independent thought is ruthlessly stifled. The chilling atmosphere Orwell created, in conjunction with his vivid descriptions, made me feel as though I were walking alongside Winston, experiencing firsthand the oppressive regime and the omnipresent threat of Big Brother.
What truly made me appreciate 1984 was its thought-provoking exploration of themes such as totalitarianism, the power of language, and the malleability of truth. Orwell's clever use of the fictional language Newspeak demonstrated how manipulation of language can control thought and shape reality, a concept that left me reflecting on the importance of linguistic diversity and freedom of expression. Moreover, the book served as a stark reminder of the dangers of totalitarianism and the importance of protecting our individual liberties.
Overall, I found 1984 to be a deeply moving and intellectually stimulating read that not only entertained me but also broadened my perspective on the world and the consequences of unchecked power.
Brave New World, by Aldous Huxley (1932)
A novel that imagines a technologically advanced society, focusing on themes of control, happiness, and the cost of progress.
From the moment I began reading Aldous Huxley's Brave New World, I was utterly fascinated by the intricate dystopian society he crafted. The novel's portrayal of a future in which humanity is conditioned to value conformity, consumerism, and superficial pleasure was as unsettling as it was thought-provoking. As I journeyed through the pages, I was both intrigued and horrified by the World State's methods of control, including the use of genetic engineering, hypnopaedia, and the drug soma.
The sterile, emotionally devoid world in which the characters lived struck me as a cautionary tale, urging readers to recognize the importance of individuality, emotional depth, and critical thought in the face of societal pressures.
Brave New World left a lasting impression on me not only because of its vivid depiction of a dystopian future but also due to the timeless themes it explores. Huxley's examination of the consequences of sacrificing truth and genuine human connection for the sake of superficial happiness and stability resonated deeply with me.
The characters' struggles to reconcile their inner yearnings with the expectations imposed upon them by their society led me to contemplate the value of authentic human experiences and the need to preserve our own capacity for critical thought and genuine emotion.
In the end, I cherished Brave New World for its capacity to challenge my beliefs, to open my eyes to the dangers of complacency, and to inspire me to stand up for the fundamental qualities that make us truly human.
The Trial, by Franz Kafka (1925)
A surreal and nightmarish exploration of bureaucracy, justice, and the nature of human existence.í
The Trial was a literary experience that deeply affected me and left a lasting impression on my psyche. From the outset, I found myself drawn into the surreal and nightmarish world of Joseph K., a man accused of a crime that is never revealed.
The novel's exploration of the bewildering, labyrinthine nature of bureaucracy and the individual's struggle for justice and understanding in an opaque and impersonal system captivated me. Kafka's distinctive writing style, with its blend of dark humor and a pervasive sense of unease, created an atmosphere that was both chilling and enthralling.
What truly made me appreciate about this book was its profound exploration of themes such as the nature of power, the role of the individual in society, and the search for meaning in an incomprehensible world. As I followed Joseph K.'s desperate attempts to navigate the mysterious legal system and clear his name, I was forced to confront my own feelings of helplessness in the face of seemingly insurmountable obstacles. The novel's ambiguous ending and its refusal to provide clear answers or resolution only heightened my sense of disquiet and led me to ponder the extent to which we can ever truly understand or control the forces that shape our lives.
The Trial was not only an engrossing and thought-provoking read but also a powerful reminder of the importance of questioning the systems that govern our existence and the need to assert our own agency in an often incomprehensible world.
The most mind-bending books challenge our perceptions of reality, explore the limits of human consciousness, and push the boundaries of conventional storytelling.
These works invite us to question our understanding of the world and ourselves, while also broadening our horizons and encouraging us to think beyond the familiar. Whether it's delving into the depths of spirituality, navigating through surreal landscapes, or unearthing the complexities of human nature, these literary masterpieces have left an indelible mark on the history of literature.
As we continue to search for new and thought-provoking books, these mind-bending classics and modern titles will undoubtedly remain a source of inspiration for readers and writers alike, as they remind us of the transformative power of literature and its ability to transport us to uncharted realms of imagination.
If you are looking for more challenging reads check out our favorite philosophical books, or the best philosophical sci-fi titles.
My profession is online marketing and development (10+ years experience), check my latest mobile app called Upcoming. But my real passion is reading books both fiction and non-fiction. I have several favorite authors like James Redfield or Daniel Keyes. If I read a book I always want to find the best part of it, every book has it's unique value.