There is a significant interest in Artificial Intelligence (AI) systems for automating decision making. While there are several AI technology solutions to choose from, there is a need to understand the fundamentals of human decision making and conceptualizing required AI system architecture. However, the challenge is: how can we conceptualize the design of an AI system architecture? This paper proposes trimodal thinking for architecting human-centric AI systems. This paper reviews dual system thinking approach, fast and slow, from the well-known book, published by Daniel Kahneman, with a specific purpose to conceptualize the human-centric AI system architecture. This review found that the fast intuitive system 1 and slow self-controlled deliberate system 2 are useful for conceptualizing the design of the AI system architecture. However, there is a need for system 3 to adjust, balance, connect, regulate and switch the control between these two systems. System 3 is critical for mitigating system 1 unconscious and system 2 conscious biases, power imbalance and noise. Relevant concepts, from principle-agent theory, homeostasis, control theory, and the atomic human, were also used to guide the proposal of trimodal thinking. Thus, this paper proposed trimodal thinking and demonstrated its use for architecting human-centric AI systems using the combination of (1) fast, (2) slow and (3) control systems. This paper also highlighted several implications for broader enterprise architecture discipline and indicated new topics across decision science and computer science areas for further research. It is anticipated that this work will provide a necessary foundation for conceptualizing technology agnostic and human-centric AI systems architecture. This will support the complex AI system explainability and transparency needs of non-technical users and technical AI system engineers.