A void sale does not establish a legally operative sale. Merely taking possession does not convert it into a valid purchase.
A defective sale of legally recognized property may have restricted effects after authorized possession, but the defect remains and the sale remains subject to unwinding.
Examples:
1. A free human cannot become saleable property.
2. Saleable goods transferred subject to an impermissible additional condition present another legal category.
3. The word 'invalid' in casual speech should not obscure these different consequences.