Why do you sometimes make decisions without knowing exactly why? How much of your everyday thoughts, feelings, and behaviors are shaped by processes you’re not aware of?
Leonard Mlodinow’s Subliminal: How Your Unconscious Mind Rules Your Behavior explains that the vast majority of our brain’s processing happens beneath the surface of awareness. This hidden mental activity shapes how we interpret our observations, form beliefs, and experience the world around us.
Keep reading for an overview of this thought-provoking book.
Overview of Leonard Mlodinow’s Subliminal
While we think we understand why we feel, think, and act the way we do, our conscious thoughts represent only the tip of the cognitive iceberg. Leonard Mlodinow’s Subliminal: How Your Unconscious Mind Rules Your Behavior (2013) explains that the vast majority of our brain’s processing happens without our awareness, in our unconscious mind, continuously shaping our experiences without our knowledge. This hidden processing shapes everything from how we interpret a friend’s facial expression to how we form our deepest beliefs about ourselves and the world.
Drawing on his background in both physics and psychology, Mlodinow synthesizes neuroscience research with real-world examples to illuminate how the unconscious mind works. The book addresses a fundamental question that has puzzled philosophers and scientists for centuries: How much control do we really have over our thoughts, feelings, and behaviors?
Mlodinow is a theoretical physicist and science writer who’s published several best-selling books, including The Drunkard’s Walk, The Grand Design (co-authored with Stephen Hawking), and War of the Worldviews (co-authored with Deepak Chopra). Subliminal was the winner of the 2013 PEN/E.O. Wilson Literary Science Writing Award.
In this overview, we’ll break down Mlodinow’s exploration of the unconscious mind to explain how unconscious processing works and why it evolved; how it shapes our sensory experiences, social perceptions, and memories; how it influences our emotions and decision-making; and how we can work more effectively with our unconscious mind.
How Scientists Understand the Unconscious Mind
For most of human history, the unconscious work of the mind remained a mystery. While Mlodinow presents unconscious processing primarily through a modern scientific lens, the idea that much of our mental activity happens outside conscious awareness has deep roots in philosophy. In the 18th century, philosopher Immanuel Kant suggested that we don’t directly experience reality but rather construct it through processes outside our conscious awareness. A century later, psychologist Sigmund Freud built on Kant’s ideas. While Kant suggested our unconscious mental processes help construct our experience of reality, Freud proposed that the unconscious mind also contains repressed memories and desires that shape our behavior.
Modern science has moved beyond Freud’s specific theories, but his core insight—that unconscious processes influence our conscious experiences—has been validated by research in psychology and cognitive science. With the arrival of neuroscience and the technology to map the brain’s activity with functional magnetic resonance imaging (fMRI) in the early 1990s, scientists confirmed the existence of the subliminal (below the threshold of conscious awareness) and began to understand how different parts of the brain handle conscious and unconscious processes.
Mlodinow explains this research has revealed that the three fundamental parts of the brain work together to process information, showing why unconscious processing plays a critical role in how we function:
- The deepest, oldest part of the brain—the reptilian brain—handles physiological processes that feel like second nature, such as breathing or activating the fight-or-flight response in dangerous situations.
- The old mammalian brain, also called the limbic system, manages the unconscious processes that enable social perception, like the split-second first impressions we form when meeting people.
- The evolutionarily newest part of the brain, the neocortex, enables our conscious thoughts and handles the actions we take with specific objectives in mind. This represents a small fraction of our brain’s activity at any given time.
Why Do We Rely Heavily on Unconscious Processing?
Modern technology has shown that our unconscious mind drives the lion’s share of everyday brain functioning, but why is this the case? Mlodinow explains that unconscious processing serves two crucial evolutionary functions: It enables us to process information more quickly and efficiently, and it helps us synthesize and interpret vast amounts of sensory data. Both of these evolutionary advantages helped our ancestors survive in a dangerous and uncertain world, and we’d struggle to navigate the complex world we live in today without these abilities.
Efficient Use of Brain Power
Mlodinow points out that we can pay attention to only a limited number of things simultaneously. So when the brain delegates routine tasks to unconscious systems, it frees up conscious attention and processing power for more demanding tasks. For instance, when you’re driving a familiar route, your unconscious mind can handle basic operations like making sure you stay in your lane and maintain an appropriate speed, which leaves your conscious mind free to plan your day, deliberate about whether you have enough time to stop for coffee, or consider a problem you’re trying to solve at work.
The brain’s ability to delegate cognitive processes to the unconscious mind also makes those processes faster and more efficient: Unconscious processes can rapidly evaluate and respond to environmental cues without the bottleneck of conscious deliberation. Mlodinow notes this proves particularly useful in situations that require fast reactions, like when we need to act quickly to avoid a threat or seize an opportunity. Mlodinow explains that our conscious processing would be too slow to respond effectively in many of these situations, and sometimes, our reliance on our unconscious abilities can make the difference between life and death.
Synthesis of Sensory Data
Unconscious processing gives us another useful tool: the ability to integrate multiple streams of information to make sense of ambiguous or incomplete data. Mlodinow explains that the unconscious mind can detect patterns, make inferences, and fill in gaps based on what we’ve learned and seen in the past. For example, when you walk into a room and sense tension between two people, your unconscious mind has already processed cues like their facial expressions, tone of voice, and positioning relative to one another before you can consciously analyze the situation. Your conscious mind will catch up, but your unconscious mind understands the situation almost immediately, which enables you to behave appropriately.
How Does the Unconscious Mind Shape Our Conscious Experiences?
Mlodinow writes that the unconscious mind shapes many aspects of our conscious experience, including our perceptions, our behavior, and our decision-making. We’ll consider some of the most important ways our unconscious processing influences what we think, do, and experience each day.
The Unconscious Mind Enhances—and Constructs—Our Sensory Experiences
Your senses are constantly collecting information that helps you understand what’s happening around you. But Mlodinow explains that your conscious experience isn’t a direct result of the raw sensory data you take in. Instead, it emerges from the unconscious mind filling in gaps and making intelligent inferences about the world around you.
Filling Information Gaps
Mlodinow notes that the sensory data you take in is incomplete, ambiguous, and distorted: Your eyes have blind spots, your vision blurs at the periphery, and your ears miss small gaps in sounds. But you don’t consciously perceive these flaws because your unconscious mind enhances and interprets the sensory information it receives and constructs a more seamless reality for you to consciously experience.
For example, Mlodinow explains that you have blind spots in your vision, caused by the point where the optic nerve attaches to each of your eyes. While these blind spots create a hole in your visual field, you probably haven’t even realized that your eyes have blind spots. That’s because your unconscious mind infers what’s likely to be in the blind spot based on the surroundings and fills in the image accordingly.
Your brain finishes filling in gaps by combining input from multiple senses and incorporating prior knowledge. For instance, when you’re speaking with a friend at a noisy restaurant, your brain might miss certain words. Your unconscious mind fills in these gaps based on your knowledge of language, context, and what you’d expect the person to say. If they say, “Please pass the s___,” your brain automatically fills in “salt” rather than “saxophone,” drawing on your previous experience at dinner tables and your unconscious mind’s assumptions about what’s most likely to be said in that setting.
Filtering Information
Your unconscious mind also plays a crucial role in determining what sensory information your conscious mind needs to be aware of. Mlodinow explains that your unconscious mind acts as a filter: amplifying or suppressing sensory signals based on how relevant or important they seem. It allows only a small portion of the sensory information you perceive to reach your conscious awareness: Otherwise you’d be overwhelmed by everything your senses perceive. For example, if you’re participating in a sport, you might not be aware of all the noise made by the crowd because your unconscious mind tunes it out and focuses your attention on things that are directly helpful to you, like what your teammates are communicating.
The Downside of Unconscious Sensory Construction
Because your brain actively constructs your perceptions based on sensory inputs combined with other factors like expectations, context, and prior knowledge, your perception isn’t always objective and accurate.
For example, let’s say you’re taste-testing various kinds of chocolates. Your brain integrates sensory information about each candy (its taste, appearance, texture, and so on) with contextual cues (like the brand, price, and packaging of each chocolate). These cues activate associations and expectations that shape your experience: Higher prices, recognizable brands, and more luxe packaging can lead you to conclude that one chocolate tastes better than another—even if they’re identical.
The Unconscious Mind Interprets Social Cues
While your unconscious mind processes all kinds of sensory information, it’s particularly important in helping you pick up on and interpret social cues—the subtle signals that help you understand and interact with other people. This sophisticated capability evolved because social connection is a fundamental human need that greatly influences our behavior and well-being.
Mlodinow explains that specialized brain regions, such as the fusiform face area (FFA), automatically analyze faces, expressions, and body language. Our unconscious mind interprets these nonverbal forms of communication effortlessly, enabling us to seamlessly navigate complex social situations that would otherwise overwhelm our conscious mind and its ability to parse what’s going on around us.
Mlodinow explains that the unconscious mind processes several key channels of social information. Let’s look at each one.
Initial Categorization
Within seconds of meeting someone, the unconscious mind automatically categorizes them by gender, age, race, and other social markers, using cues like facial characteristics, clothing, and even environmental context. For instance, when you walk into a business meeting, your brain rapidly processes whether someone is likely an executive (based on their age, attire, and where they’re sitting) or a junior employee.
Facial Expressions
Our unconscious mind also processes facial expressions—a universal and innate way for humans to express basic emotions like happiness, fear, and anger. Mlodinow explains that our facial muscles are governed by separate voluntary and involuntary neural pathways, which enables the unconscious minds to quickly distinguish genuine “Duchenne smiles” involving the eye muscles from forced smiles using only the mouth muscles.
Vocal Qualities
While we consciously focus on the words another person is saying, our unconscious minds are processing subtle cues from their voice. These signals provide a continuous undercurrent of information that shapes our impressions of and relationships with other people. Studies show we can judge traits like dominance, trustworthiness, and even fertility from voice pitch, speech rate, and tone.
Body Language
The unconscious mind also processes nuances of body language, including gestures, posture, eye contact, and use of personal space. This nonverbal “conversation” reveals social dynamics and hierarchies. For example, people automatically adjust their eye contact patterns based on perceived status—those who see themselves as having higher status tend to make more eye contact when speaking than listening, while those who feel they have lower status do the opposite.
The Dark Side of Unconscious Social Processing
While this sophisticated system of nonverbal communication helps us navigate social situations and build relationships, our unconscious social processing can also lead to problematic biases. Our tendency to rapidly categorize people—which likely evolved as a survival mechanism—can create an “us vs. them” mentality where we unconsciously perceive our in-group as superior and out-groups as inferior or threatening. This means we often:
- Perceive members of the same category as more alike than they really are
- Exaggerate differences between groups
- Automatically associate people with stereotypical traits based on surface-level characteristics
- Make snap judgments that can fuel prejudice and discrimination
While these quick categorizations might have aided survival in prehistoric times, in modern society they can lead to harmful biases based on differences like race, ethnicity, or religion. Mlodinow explains that understanding these unconscious social biases is the first step toward consciously counteracting them.
The Unconscious Mind Shapes Our Emotions
Mlodinow explains that emotions aren’t simply triggered by external events, as we often assume. Instead, our unconscious mind constructs them through a complex interplay between physiological responses and contextual information. This insight builds on a theory first proposed by psychologist William James, who suggested that we first experience bodily changes (like increased heart rate), and then our interpretation of those changes creates the emotional experience (like fear or joy).
The reconstructive nature of emotions can lead to what scientists call “emotional illusions”: situations where we misinterpret our physiological state based on the context around us.
For example, imagine your heart is racing from climbing stairs when you encounter an angry colleague. Your unconscious mind might mistakenly attribute your elevated heart rate to the social interaction, intensifying your emotional response to the colleague’s anger. This phenomenon was demonstrated in a classic study: When participants were given adrenaline (which increases heart rate and arousal) without knowing it, they interpreted their physiological arousal according to social cues in their environment—feeling either happiness or anger depending on how others around them were behaving.
Understanding that emotions are reconstructive processes shaped by unconscious interpretation helps explain why our emotional responses can sometimes seem disproportionate or disconnected from the situation at hand. It also suggests why the same physiological state (like the butterflies in your stomach) might be interpreted as anxiety before a public speech but as excitement before a first date—your unconscious mind uses context to determine which emotion you experience.
The Unconscious Mind Reconstructs Our Memories
While we often think of memories as perfect recordings of past events, Mlodinow explains that our memories are actually dynamic reconstructions shaped by our unconscious mind. Rather than acting like a video camera that faithfully captures and stores every detail, our memory system is more like a storyteller that recreates events each time we recall them.
Mlodinow explains that the reconstructive nature of memory serves an adaptive purpose: Instead of storing every detail of our experiences (which would be overwhelming and inefficient), our brains typically preserve the gist of events and then fill in specific details based on our expectations and prior knowledge. However, this process also makes our memories susceptible to distortion.
Memory distortion typically follows predictable patterns:
- Simplification: Complex events get streamlined into simpler narratives.
- Rationalization: Confusing or ambiguous details are reinterpreted to make more sense.
- Integration: New information gets incorporated into old memories.
- Consistency: Memories tend to shift to better align with our current beliefs and understanding.
Many studies demonstrate how easily memories can be altered or even fabricated. Even our most vivid and emotionally charged memories can be unreliable. This has important implications for how we think about our past experiences and how much we should trust our recollections, especially in high-stakes situations like legal testimony or major life decisions.
The Unconscious Mind Influences Our Decision-Making
While we like to think of ourselves as rational decision-makers who carefully weigh the evidence before reaching conclusions, Mlodinow reveals that our unconscious mind plays a powerful role in shaping our judgments—often before our conscious mind even begins its analysis. Our unconscious rapidly evaluates options based on instinctive appraisals, emotional associations, and implicit memories, creating biases that influence our eventual decisions.
One of the most powerful ways our unconscious mind shapes decision-making is through what psychologists call “motivated reasoning”—our tendency to process information in ways that support our existing beliefs and desires. Like skilled lawyers arguing a case, our minds unconsciously seek out evidence that supports our preferred conclusions while discrediting contradictory information. This happens through several mechanisms:
- Adjusting Standards: We scrutinize evidence that challenges our beliefs more rigorously than evidence that supports them.
- Selective Attention: We give more weight to information that aligns with our desired conclusions.
- Biased Interpretation: We interpret ambiguous information in ways that fit our preferences.
- Gap-Filling: When information is missing, we invent explanations that align with our existing beliefs.
This tendency toward motivated reasoning likely evolved as an adaptive mechanism—maintaining positive self-beliefs and confidence in our decisions would have helped our ancestors persist in challenging situations. However, in modern contexts, it can lead us to maintain biased views while believing we’re being completely objective.
For example, when reading about a controversial political issue, we might thoroughly fact-check articles that challenge our existing views while accepting supporting articles at face value, dismiss statistics that contradict our position as “flawed research” while treating favorable statistics as definitive proof, and fill in gaps in our understanding with assumptions that conveniently align with what we already believe.
How Can You Work With Your Unconscious Mind?
While we can’t directly control our unconscious processes, Mlodinow explains that understanding them can help us make better decisions and align our behavior more closely with our conscious goals and values. As he emphasizes, the goal isn’t to eliminate unconscious influences—they’re an essential part of how our brains work—but rather to understand them better so we can make more informed choices about when to trust our automatic responses and when to be more deliberate. We’ll examine the key strategies that Mlodinow recommends to work more effectively with your unconscious mind:
Recognize Your Gut Feelings
First, Mlodinow says to pay attention to your intuitions and gut feelings, even when you can’t immediately rationalize them. Your unconscious mind often picks up on subtle patterns and cues that your conscious mind hasn’t yet processed. For instance, you might have an inexplicable feeling of unease during a job interview. While you can’t consciously pinpoint why, your unconscious mind might be picking up on subtle inconsistencies in the interviewer’s body language or tone that suggest they’re not being entirely truthful about the role. However, don’t simply accept these feelings uncritically—use them as data points to investigate further.
Question Your Automatic Judgments
Second, Mlodinow recommends that, when you’re making important decisions, you should pause to examine your initial reactions. Are you making snap judgments based on unconscious categorizations or biases? Give your conscious mind time to evaluate options rationally, especially in situations involving:
- First impressions of people
- Decisions under time pressure
- Emotionally charged or highly personal issues
Counter Your Tendency to Use Motivated Reasoning
Third, Mlodinow explains that it’s important to consciously counter your unconscious mind’s preference for motivated reasoning. To combat your mind’s tendency to favor information that confirms your existing beliefs:
- Actively seek out contradictory evidence.
- Consider alternative perspectives, especially from credible sources that challenge your views.
- Question your thought process and assumptions, particularly when evaluating issues that matter to you personally.
Cultivate Better Self-Awareness
Fourth, Mlodinow recommends cultivating habits that help you notice the influence of unconscious processes, building a better awareness of what your unconscious mind is doing and how deeply it influences what you think, do, and experience:
- Practice mindfulness meditation to become more attuned to your thoughts and feelings.
- Pay attention to nonverbal cues in social situations.
- Notice patterns in your emotional reactions and decision-making.
- Embrace ambiguity rather than rushing to black-and-white judgments.
Diversify Your Experiences
Finally, Mlodinow points out that your unconscious mind can become entrenched in familiar patterns, so he recommends that you deliberately expose your mind to a wide variety of different experiences. He recommends seeking out:
- Different perspectives and viewpoints
- New experiences and environments
- Diverse social connections
- Unfamiliar information sources
For example, if you typically socialize with people who share your professional background and political views, your unconscious mind might develop overly rigid patterns for categorizing and judging others. By deliberately expanding your social circle to include people with different life experiences and viewpoints, you can help your unconscious mind develop more nuanced and flexible ways of processing social information.
