The 16 personality types make more sense when you understand what is running underneath them. Every type has a stack of four cognitive functions — specific mental processes that determine how it takes in information, makes decisions, and relates to the world.
The eight functions
There are eight cognitive functions in total — four introverted, four extroverted. Each one describes a distinct way of processing information or making judgments.
Perceiving functions (how you take in information)
- Introverted Intuition (Ni) — Pattern recognition and long-range vision. Sees what is coming before it arrives. Convergent, focused, symbolic.
- Extroverted Intuition (Ne) — Possibility-spotting and lateral connection. Sees what could be. Divergent, generative, associative.
- Introverted Sensing (Si) — Detailed memory and precedent. Compares the present to a rich internal library of past experience.
- Extroverted Sensing (Se) — Present-moment awareness and physical experience. Fully engaged with what is happening right now.
Judging functions (how you make decisions)
- Introverted Thinking (Ti) — Internal logical frameworks. Needs to understand exactly how something works before accepting it as true.
- Extroverted Thinking (Te) — External organisation and efficiency. Measures by results, structures systems, produces measurable outcomes.
- Introverted Feeling (Fi) — Core values and personal moral compass. Filters decisions through a deeply held, internally developed sense of what matters.
- Extroverted Feeling (Fe) — Social harmony and collective emotional awareness. Attuned to group dynamics and the emotional needs of others.
Your function stack
Each personality type uses four of the eight functions, arranged in a stack: dominant, auxiliary, tertiary, and inferior.
Your dominant function is what you rely on most — the process that feels most natural and energising. Your auxiliary supports and balances it. Your tertiary and inferior functions are where you are weakest, and where stress tends to surface.
For example, an INTJ’s stack runs: Ni (dominant) — Te (auxiliary) — Fi (tertiary) — Se (inferior). An INFP’s stack runs: Fi (dominant) — Ne (auxiliary) — Si (tertiary) — Te (inferior). Same four letters almost, completely different architecture underneath.
Why this matters
Cognitive functions explain something the four-letter type code alone cannot: why people of the same type can seem very different from each other, and why certain tasks feel effortless while others are exhausting even when you are technically capable of doing them.
An INFP struggling with project management is not failing at discipline. They are running their inferior function — Extroverted Thinking — which is the least developed process in their stack. Knowing this does not eliminate the struggle, but it stops you from treating a neurological reality as a character flaw.
The personality test identifies your type and gives you your function stack. If you have not taken it yet, that is the starting point.