成唯識論述記 1.370

1.370

述曰：此中二難，體用相例。量云：用應常有；許不離體故；如體。體應非常有；許不離用故；如用。外人計體不離於用故，為此因。

The Commentary states: Herein are two objections, drawing analogies between substance and function. The syllogism: 'The function should be permanently existent; because it is admitted not to be separate from the substance; like the substance. The substance should be non-permanent; because it is admitted not to be separate from the function; like the function.' The outsiders impute that the substance is not separate from the function, which therefore serves as this reason.