Sound, smell, taste, image, touch, sleep.
Can you think without clinging to these forms?
A thought without shape is rare,
Knowledge of Tao rarer still.

Our mind needs to cling to some object in order to function in its usual modes. If you look at your memories, you will find that most are tied to some sensory image. The thought of being in the country brings up a certain fragrance. You “see” relationships in a certain way. We may do math problems, or compose something to say to our companions, but we will still think in numbers and words.
Some people make the mistake of rejecting this type of thinking, but we need to use these modes in order to function in the everyday world. When it comes to knowing Tao, thought tied to sensory images is not enough to bring complete realization. Dualistic thinking cannot be used to know Tao. But don’t discard it as long as ordinary functioning in the world is necessary.

When one meditates, one must use an aspect of consciousness that does not cling to external forms. This type of consciousness is beyond the senses. Some call these states of mind superconsciousness, samadhi, nirvana, or enlightenment. These are mere names. All that matters is getting to these states. Then all labels fall away.