堪輿家相信世間萬物由氣化成，天地初開混沌之氣分清濁，天升地降成陰陽，乾坤兩儀。風水之理氣充斥於人類所生存之空間，流走於大地、山川、海洋。人類之建築物受到理氣之影響而產生吉凶福禍。建築物在不同之元運，不同之方向建成時，理氣會經納氣口進入建成的空間，產生不同之氣場變化，繼而流走八方。所以陽宅在不同的年份及方向建成，會自有不同納得的理氣。當然有不同的卦象產生。這新卦象到底是吉是凶，便要靠理氣盤及外巒頭斷之。理氣為無形無色無味無態。世人得知理氣之存在，是靠它對人和事影響後，驗證回來。例如人類居住在納得病符理氣的房間內，便會得疾病等情況。

理氣口訣

隨氣而動，隨地而行，隨物而感，隨屋而附，隨人而應。

古賢之理氣口訣中亦說明了理氣之特性，理氣會隨風而動，才會有能量之產生。隨地而行，才會有納氣之機會。隨物而感，才會有巒頭之影響。隨屋而附，才會有陽宅風水之好壞。隨人而應，人才會去關心風水。總之，理氣可謂，風水之基本也。

Li Qi

Kan Yu masters believed that all matters in the world arises from Qi. When our planet Earth was first formed, it was filled with Qi. Polarity was then generated from the Qi. The Yang Qi ascended to form the heaven, while the Yin Qi descended to become the earth. This constitutes the Qian (positive) and the Kun (negative) poles. In feng shui, it is believed that Qi fills our environment. It flows on earth, moves among the mountains, the rivers and oceans. This Qi will have effect on our buildings resulting in auspiciousness and fortune or otherwise. Buildings constructed at different time, or having different orientations are receiving different kinds of Qi or vital energies through their door openings. As a result, it will produce different effect as reflected by the various trigram features. Whether it is auspicious or not is judged by the pattern in the flying star chart, together with the external and internal arrangements. Qi is abstract. It does not have a shape, colour, smell or texture that one can feel. However, one can aware its existence by observing its effect on people and their accomplishment. For example, people who live in a house that has the trigram of illnesses will become sick more easily.

The Secret of Li Qi states that

Qi moves in the wind. It creeps on ground. It can feel the objects that it encounters. It can attach to houses and exert its effect on people spending time there.

The sages have described the features of Qi in the above secret. It is believed that Qi moves in the wind, so it can be of different energy strength, being weak or strong. It flows on ground, so it can enter a newly constructed building. It can feel the objects in the environment. Therefore, its nature is affected by the features in the environment. It attaches to houses, so it will affect their feng shui. Its effect is on people, so that is why people care about feng shui. In short, Qi is the foundation to feng shui studies.