One time, a monk asked Chan master Shishuang Qingzhu (807–888), "I heard that buddha-nature is like space; is that correct?" Shishuang replied, "It's present when you sleep; absent when you sit." Similarly, when asked by a monk whether a dog has buddhanature or not, Chan master Zhaozhou Congshen (778–897) said, "No!" These two examples are like a fish asking another fish, "I heard that fish swim in water. Is that correct? There are such things as fish and water, right?" Ridiculous questions deserve ridiculous answers.
Buddhanature is our true nature, already free from self (Skt. atman), vexations (Skt. klesas), and delusions (Skt. avidya). The personal experience of this freedom is called awakening (Skt. bodhi). Mahayana scriptures have already clarified that buddhanature is present everywhere, in all beings, and have provided many metaphors for it (e.g., spacious and vast like the sky or ocean)—so why ask?
We ask because we are trapped in our narrow, myopic perceptions, seeing only good and bad, joy and sorrow, right and wrong, success and failure, having and lacking, fair and unfair, self and other. The self, or the "me, I, mine," come into being when we are caught up with these perceptions. This is delusion—it vanishes when we personally experience the emptiness of these perceptions—when we see through the veil of these constructs. This is wisdom, awakening. A fish doesn't have to imagine the "water" in swimming—it just swims. It's through swimming that the water is experienced. The important thing is to keep swimming. (Read more here)
