I've gotten a couple of questions about my use of the word "cell" when talking about the nature of sensation and perception, and whether it violates the hierarchy of knowledge. Since philosophy is the necessary foundation on which we build specialized sciences, isn't it wrong to base the philosophical understanding of sensations on the idea of cells, which are a scientific discovery?
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    Yes. But that is not how I use the term.
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    As Ayn Rand pointed out, knowledge is contextual, and a single word can have multiple meanings, depending on the context in which it's used. Due to the intimate relationship between science and philosophy, it is not unusual for different concepts, some pertaining to philosophy, and some to science, to share the same word.
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    The atom is good example of this phenomena. The word was originally coined by Democritus, a Greek philosopher who believed that all matter must be made up of indivisible parts. Millenia later, when the chemist John Dalton identified that substances were made up of discrete particles of specific elements, he believed to have found these indivisible "building blocks", and called his discovery "atoms". This was a mistake, and we ended up with two different ideas: the philosophical atom, and the scientific "atom", which we now know to be made up of subatomic particles.
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    The same is true of cells, although the term's history is even murkier. With the development of microscopes, 19th century biologists identified little "compartments" that made up every living being. In response to that discovery, they developed the "cell theory", which was a mix of philosophy and biology. On one hand, they formulated the philosophical idea that living beings are an integration of smaller, living units - the philosophical cell. On the other, they assumed that those particular microscopic "compartments" were that basic unit - the biological cell. 
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    We now know that the biological cell is not the basic unit of living beings, as they are, themselves, composed of smaller, living units. The philosophical cell, however, is the idea that living beings are an integration of smaller parts, also capable of self-generated, goal directed action - whatever these parts might be. This philosophical idea is valid, and independent of any specialized knowledge, as I will explain in the next post.