The classic and most frequently cited example of tone has to do with the difference in meaning between "and" and "but". According tofrege these two words can be interchanged without affecting the truth-value of an entire sentence in which they occur. He is thinking, of course, of instances in which they function as sentence connectors. In such cases their truth-tables are identical. "It is cold outside and Smith is happy" is true, or false, under the same conditions as "It is cold outside, but Smith is happy". They are thus held to possess the same sense (Sinn). The same holds for "Although it is cold outside, Smith is happy". All three are symbolized in logical idiom as "P & Q". But, as Frege rightly says, they are not synonymous.