Passing an iterator

The code

Table[i, {i, 5}]

produces the output

{1, 2, 3, 4, 5}

whereas the code

x = {i, 5};
Table[i, x];

produces an error, namely

Table::itform: Argument x at position 2 does not have the correct form for an iterator.

Why, and how do I fix this?

Answer

Table has attribute HoldAll. This means its arguments are left unevaluated:

Attributes[Table]
(* {HoldAll, Protected} *)

Using an Evaluate will force the evaluation order to be as you desire:

x = {i, 5};
Table[i, Evaluate@x]

(* {1, 2, 3, 4, 5} *)