Sitting across from a 22-year-old account manager in my agency office, I watched him struggle with the same challenge I’d faced at his age. He had the strategic thinking down but couldn’t quite connect with clients emotionally yet. Ten years later, he’d become one of our most effective leaders, naturally balancing analysis with empathy. The transformation wasn’t accidental. His brain had been developing cognitive functions on a predictable timeline I’d learned to recognize after managing teams for two decades.
Your cognitive functions develop in a specific sequence that explains why a 25-year-old INTJ operates completely differently than a 45-year-old with the same personality type. The dominant function develops by age 7, the auxiliary by age 20, the tertiary in your 30s and 40s, and the inferior function at midlife or later. This developmental timeline transforms how you process information, make decisions, and relate to others at each life stage.
The progression from cognitive simplicity to complexity mirrors what I observed across hundreds of client relationships. Young professionals relied heavily on one or two mental processes. Senior executives accessed a broader cognitive toolkit developed over decades. This wasn’t just experience accumulating; it was their brains building new pathways for processing information and relating to others.
What Happens During Early Cognitive Development?
Before age 7, children experiment with all eight cognitive functions, trying each one for fit. An INFJ child might show glimpses of their future Introverted Intuition alongside moments of Extraverted Sensing or Introverted Thinking. The brain tests different processing styles, determining which feel most natural and effective.
By age 7, your dominant function emerges as the primary way your mind operates. Children begin to prefer using their natural dominant function to take in information or make decisions, and this becomes the prevailing aspect of their personality. An INTJ child starts showing strong pattern recognition and future-oriented thinking. An ESFP child demonstrates immediate sensory awareness and spontaneous engagement with their environment.
- Pattern testing phase (ages 0-7) – Your brain experiments with different cognitive approaches to determine which processing styles feel most natural and effective for your unique neural wiring
- Dominant function crystallization – Around age 7, one cognitive function emerges as your primary mental highway, the processing style you’ll rely on most heavily throughout life
- Natural preference establishment – You begin defaulting to your dominant function for major decisions and reverting to it automatically under stress or pressure
- Foundation building period – Your brain prioritizes building neural pathways that support your dominant function, making it feel effortless while other functions remain underdeveloped
During my agency years, I learned to spot these dominant functions in action. The analyst who naturally synthesized market data into strategic frameworks was likely using Introverted Intuition. The creative director who excelled at reading room dynamics and adjusting presentations in real-time probably led with Extraverted Feeling. Their careers would build on these foundational processing styles.
The dominant function operates like a mental highway you travel most frequently. It feels effortless because your brain has prioritized building neural pathways supporting this particular cognitive process. You trust this function implicitly, consulting it for major decisions and defaulting to it under stress. Developing your other functions requires conscious effort precisely because they don’t enjoy this automatic prioritization.
How Does Your Auxiliary Function Develop Through Your Twenties?
Between ages 13 and 21, your auxiliary function develops to support and balance your dominant. An INTJ’s Extraverted Thinking emerges to give their internal insights external expression. An INFP’s Extraverted Intuition awakens to complement their deep internal values with exploration of possibilities.
This developmental window explains why teenagers and young adults often seem caught between two different operating modes. They’re literally building a second major cognitive pathway. The 19-year-old intern who showed brilliant strategic insights but couldn’t yet translate them into actionable project plans was working through this exact transition. Her Introverted Intuition was strong, but her Extraverted Thinking still needed development.
- Balancing mechanism development – If your dominant function gathers information, your auxiliary helps you make decisions using that data; if your dominant makes judgments, your auxiliary ensures you take in sufficient information first
- Public face formation – For introverts, the auxiliary function becomes your extraverted interface with the world while your dominant continues operating internally and privately
- Cognitive partnership establishment – These two functions handle roughly 90% of your mental processing by your late twenties, creating your recognizable personality type pattern
- Professional competence foundation – Most career success in your twenties builds on effectively using your dominant and auxiliary functions in complementary ways
The auxiliary function serves a critical balancing role. Studies suggest people without a reasonably strong auxiliary function to complement their dominant may have problems functioning effectively. You need both perception and judgment working together.
For those who identify as introverted, the auxiliary function becomes your public face. Your dominant operates internally, processing information privately. Your auxiliary, being extraverted, shows the world how you engage. An INFJ’s Extraverted Feeling creates their warm, interpersonally skilled exterior even though their dominant Introverted Intuition does its work beneath the surface. Understanding how cognitive functions operate in workplace settings helped me decode these dynamics in my teams.
Most people in their twenties have developed their dominant and auxiliary functions to the point where their personality type becomes recognizable. These two functions handle roughly 90% of their cognitive processing. The real work of expanding mental flexibility comes later.
What Changes When Your Tertiary Function Emerges in Your Thirties?
Between ages 21 and the mid-40s, your tertiary function begins emerging. This third cognitive process rounds out your mental toolkit, though it never achieves the strength of your first two functions. An INTJ’s Introverted Feeling starts developing, allowing access to personal values and emotional nuance that felt foreign in their twenties. An ENFP’s Thinking function strengthens, enabling more logical analysis alongside their natural intuitive exploration.
I noticed this shift distinctly in my late 30s. My dominant Introverted Intuition and auxiliary Extraverted Thinking had served me well in strategic roles and client presentations. The emergence of my tertiary Introverted Feeling opened new dimensions in leadership. I could finally access the emotional intelligence that had always felt slightly out of reach. Client relationships deepened. Team dynamics became clearer. I wasn’t fundamentally changing my type; I was adding new processing capabilities.
- Expanded processing range – Your tertiary function adds a third cognitive tool to your toolkit, increasing the variety of situations you can handle effectively without requiring tremendous effort
- Leadership capability growth – Many professionals experience career advancement during tertiary development as they become capable of managing more complex, multi-dimensional challenges
- Interest diversification – New hobbies, activities, or perspectives that didn’t appeal earlier often reflect your developing tertiary function seeking expression and practice
- Emotional intelligence enhancement – Whether your tertiary function is Thinking or Feeling, its development typically improves your ability to understand both logical and emotional dimensions of situations
The tertiary function often manifests as newfound interest in activities or perspectives that didn’t appeal earlier. The analytical executive suddenly takes up painting. The empathetic counselor develops fascination with data analysis. These aren’t random midlife hobbies; they’re expressions of developing cognitive processes. Tertiary function development represents your brain’s natural maturation timeline.
Proper tertiary development requires patience. This function won’t ever match your dominant or auxiliary in ease or reliability. Trying to force rapid development often backfires, creating stress and burnout. The healthier approach involves gradual exposure, treating tertiary function use as skill-building rather than personality transformation.
During this period, research shows individuals generally experience increases in conscientiousness, agreeableness, and emotional stability as part of what psychologists call the maturity principle. These broader personality shifts coincide with cognitive function development, creating a more balanced and adaptable psychological profile.
Why Is Midlife Inferior Function Integration So Challenging?
Your 40s through 70s bring the most challenging developmental task: integrating your inferior function. This fourth process represents your least developed cognitive style, the one that feels most foreign and uncomfortable. An INTJ must grapple with Extraverted Sensing, becoming more present and aware of immediate sensory experience. An ESFP faces Introverted Intuition, learning to see patterns and consider future implications.
Some researchers suggest the emergence of inferior functions at this life phase may be responsible for what we commonly call the midlife crisis. Suddenly confronting a completely underdeveloped part of yourself creates discomfort. The strategic thinker realizes they’ve missed years of sensory pleasure. The spontaneous personality recognizes they’ve avoided long-term planning to their detriment.
Leading client teams through corporate transitions in my 50s, I watched numerous executives face this developmental reckoning. The CFO who’d spent 30 years in spreadsheets suddenly wanted creative projects. The charismatic CEO who’d built the company on relationships began craving solitary analytical work. These shifts reflected their brains finally developing pathways they’d largely ignored for decades.
- Cognitive discomfort phase – Your inferior function feels foreign and exhausting to use, creating psychological tension as you recognize a completely underdeveloped aspect of yourself
- Identity questioning period – Many people experience what appears to be personality instability as they explore cognitive territories they’ve avoided for four decades
- Integration versus mastery – The goal isn’t to make your inferior function strong, but to develop enough competence to access it when circumstances absolutely require it
- Wisdom through wholeness – People who successfully integrate their inferior function demonstrate remarkable cognitive flexibility and psychological maturity in later adulthood
The inferior function never becomes a strength in the traditional sense. Even with development, it remains your weakest cognitive process. The goal isn’t mastery but integration. Can you access this function when circumstances require it? Can you recognize when others are using it skillfully? Can you tolerate the discomfort it creates?
By later adulthood, people who’ve developed all four functions demonstrate remarkable cognitive flexibility. They rely on their dominant and auxiliary for most tasks but can temporarily shift to their tertiary or inferior when needed. From midlife until death, individuals have access to all four functions and use them in a more disciplined, differentiated manner. The personality type continues asserting itself, but with greater adaptability.
What Factors Speed Up or Slow Down Your Development?
Individual development timelines vary significantly based on several factors. Childhood environment plays a crucial role. If the use of your dominant and auxiliary functions were not supported by your environment, they will press to reach the surface like a beach ball held under water, and you may feel that tension. Children raised in families or schools that valued their natural processing style develop more smoothly than those forced to suppress their cognitive preferences.
Life experiences accelerate or delay function development. Trauma, major transitions, and challenging relationships can disrupt the typical timeline. Traumatic experiences sometimes lock people into relying exclusively on their dominant function as a coping mechanism, preventing auxiliary development until they process those experiences.
- Environmental support factors – Family, school, and work environments that encourage your natural processing style facilitate smoother development than those requiring constant cognitive suppression
- Professional pressure accelerators – Career roles that demand specific functions force faster development; the INTJ therapist develops Feeling faster than one in pure strategy consulting
- Trauma-related delays – Significant stress or trauma can lock people into relying exclusively on their strongest function as protection, preventing normal developmental progression
- Deliberate development efforts – Conscious practice using weaker functions in low-stakes situations can accelerate development beyond natural timelines
- Resistance consequences – People who refuse tertiary and inferior function development become increasingly rigid and unable to adapt when circumstances demand cognitive flexibility
Career choices shape cognitive development patterns. The INTJ who becomes a therapist develops their Introverted Feeling faster than one who remains in pure strategy consulting. The ESFP who goes into data analysis forces their Introverted Thinking to develop earlier than typical. Professional demands create pressure for developing functions that might otherwise remain dormant longer.
Deliberate development efforts can accelerate the process. Once you understand which functions need strengthening, you can create situations that require their use. The strategic thinker who volunteers for roles requiring emotional intelligence builds their Feeling function faster. The spontaneous personality who commits to long-term project planning develops their Intuition more quickly. Research supports the idea that personality can change as a result of both intrinsic factors like genetics and extrinsic factors like the environment around us.
Resistance to development creates problems. People who refuse to develop their auxiliary function often struggle with decision-making or information gathering. Those who avoid their tertiary and inferior functions become psychologically rigid, unable to adapt when circumstances demand different cognitive approaches. Getting stuck in cognitive loops happens when you rely exclusively on your strongest functions.
How Can You Identify Development Stages in Yourself and Others?
Identifying where someone falls in their cognitive development reveals important information about their capabilities and needs. The 24-year-old with strong dominant function but developing auxiliary requires different support than the 42-year-old working on tertiary integration. Managing Fortune 500 accounts taught me to assess development stages quickly, adjusting communication and expectations accordingly.
Young adults (early 20s) typically show two-function operation. They excel at tasks aligned with their dominant and auxiliary but struggle when situations demand their tertiary or inferior. Expecting well-rounded cognitive flexibility at this age sets people up for failure. Better to leverage their natural strengths and provide support for developing areas.
- Dominant function assessment – This feels completely effortless and automatic; you use it without conscious thought and trust it implicitly for major decisions
- Auxiliary function evaluation – Takes slight mental effort but feels reliable and supportive; you can use it effectively when you focus on it
- Tertiary function recognition – Demands conscious attention and practice but yields good results when you work at it; feels like a learnable skill
- Inferior function identification – Feels foreign, exhausting, and uncomfortable even when you access it successfully; requires significant energy to use
Professionals in their 30s and 40s display increasing cognitive complexity. Their tertiary function begins contributing meaningfully, expanding their range of effective responses. This period often brings career advancement as people can handle more varied situations. The account director who previously excelled only at client relationships suddenly manages both relationships and strategic planning. That’s tertiary development in action.
Midlife and older adults demonstrate either remarkable flexibility or stubborn rigidity depending on whether they’ve embraced development. Those who’ve integrated all four functions handle complex situations with grace, switching between different cognitive modes as circumstances require. Those who’ve resisted development become increasingly brittle, insisting their way is the only effective approach.
You can assess your own development by noticing which functions feel effortless versus uncomfortable. Your dominant requires zero thought; you use it automatically. Your auxiliary takes slight effort but feels reliable. Your tertiary demands conscious attention but yields results with practice. Your inferior feels foreign and exhausting even when you access it successfully. Honest assessment of these comfort levels reveals your current developmental stage and next growth areas.
How Does This Apply to Your Professional Life?
Understanding cognitive development transforms how you approach career decisions, team building, and professional relationships. When hiring, I learned to match roles with developmental stages. Complex leadership positions requiring four-function flexibility went to experienced professionals in their 40s and 50s. Specialist roles leveraging one or two functions suited younger employees still building their cognitive toolkit.
Training programs work better when they account for development stages. Teaching a 25-year-old to use functions they haven’t developed yet wastes everyone’s time. Focus on strengthening their dominant and auxiliary while building awareness of tertiary function potential. Save inferior function work for later career stages when their brain has completed sufficient development to make that integration possible.
- Age-appropriate role matching – Specialist positions work best for professionals in their twenties; complex leadership requiring four-function integration suits those in their forties and fifties
- Developmental training design – Programs should strengthen existing functions in younger workers and explore function expansion for mid-career professionals
- Transition timing recognition – Career shifts often align with function development; the 40-something consultant moving to teaching may be following tertiary emergence
- Collaboration adjustment strategies – Expectations and support should reflect others’ developmental stages rather than assuming uniform cognitive capabilities across age groups
Career transitions often align with developmental milestones. The consultant who shifts to teaching in their 40s may be following tertiary function emergence. The detail-oriented professional who starts a creative venture at 50 could be answering inferior function calls. These transitions aren’t midlife crises; they’re natural expressions of cognitive maturation. Career satisfaction often improves when professional roles align with current developmental stage.
Collaboration becomes more effective when you recognize others’ developmental stages. The young analyst with brilliant insights but poor execution isn’t lazy; their auxiliary function is still developing. The senior executive who suddenly wants hands-on project work isn’t having a breakdown; their inferior function is demanding attention. Adjusting expectations and support based on these developmental realities creates stronger working relationships.
Personal development goals should reflect your current stage. In your 20s, focus on strengthening your auxiliary to complement your dominant. In your 30s and 40s, explore tertiary function development through new activities and perspectives. At midlife and beyond, cautiously approach inferior function integration, accepting that discomfort comes with this territory. Research on lifespan personality development confirms that development is a lifelong process that can help you overcome challenges throughout your life.
Why Understanding This Development Timeline Matters
Cognitive function development provides a roadmap for personal growth that honors your natural processing style while expanding your capabilities. You’re not trying to become a different type or develop all functions equally. You’re building on your innate strengths and gradually adding complementary processing abilities at developmentally appropriate times.
This framework explains many experiences that might otherwise seem confusing. The 35-year-old who suddenly feels drawn to activities they previously dismissed isn’t being inconsistent; they’re responding to tertiary function development. The 50-year-old who questions lifelong assumptions isn’t having a crisis; they’re integrating their inferior function. These shifts represent healthy maturation, not personality instability.
Understanding developmental timelines also reduces frustration with yourself and others. A 23-year-old can’t access cognitive flexibility that requires functions not yet developed. A 60-year-old won’t dramatically change processing styles that have strengthened over six decades. Accepting these developmental realities creates realistic expectations and reduces pointless struggle.
The most effective professionals I’ve worked with understood their developmental stage and worked with rather than against it. They leveraged their strongest functions for maximum impact and gradually built weaker ones through deliberate practice. They didn’t try to be someone they weren’t, but they also didn’t limit themselves to narrow cognitive patterns. They grew in directions their brain was ready to support.
Your cognitive functions will continue developing throughout your life if you create conditions supporting that growth. Challenge yourself to use less-developed functions in low-stakes situations. Seek relationships and experiences that require cognitive flexibility. Notice when you’re stuck in rigid patterns and consciously shift to different processing modes. Understanding all aspects of your cognitive stack, including shadow functions, provides additional context for this lifelong developmental process.
After leading teams for over two decades, I’ve watched cognitive development play out in hundreds of professionals. The pattern holds remarkably consistent across different personality types and industries. Those who embrace this developmental arc and work with their brain’s natural timing achieve more sustainable growth than those fighting against it. Your cognitive functions develop on a predictable timeline. Understanding that timeline lets you support rather than resist your brain’s natural maturation process.
Explore more insights on personality types in our complete MBTI General & Personality Theory Hub.
About the Author
Keith Lacy is a person who identifies as introverted and has learned to embrace his true self later in life. With a background in marketing and a successful career in media and advertising, Keith has worked with some of the world’s biggest brands. As a senior leader in the industry, he has built a wealth of knowledge in marketing strategy. Now, he’s on a mission to educate people of all personality types about the power of introversion and how understanding this personality trait can access new levels of productivity, self-awareness, and success.
