reduced density matrices (or improper mixtures) are extremely different. In the first case, the systems described always possess well-defined quantum states, even though these might not be known to us. In the second case, if the subsystem one wants to describe is entangled, it simply does not possess a well-defined state. As a result, $\rho_A$ cannot be considered to represent the state of the system, so it becomes merely a mathematical tool to encode information regarding the behavior of $A$ in *measurement* situations. That is, it is only an instrument useful to make predictions regarding the results one expects to find while performing measurements on the system in question, assuming, of course, both the Born rule and the projection postulate.

Now we are in position to evaluate if, as advertised, decoherence is in deed able to suppress macroscopic interference and choose a preferred basis. We will discuss each of these in turn.

Suppression of interference {#si}
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The starting point of the claim that decoherence explains the absence of macroscopic interference, is the fact that every object inevitably interacts with its environment and, furthermore, that through such interaction the environment “obtains certain information” regarding the system. Moreover, it is claimed 