So .. another speech affectation

"Can you explain why you did this?"

"So, we thought that.."

Have you noticed? When asked a question, for a growing number of people the word 'Because' seems to have disappeared from their lexicon, to be replaced by the word "So.."

I first noticed it with politicians (I won't name them). However it now seems to be permeating every day speech.

What ever happened to saying "Because .."?