I studied Philosophy and Metaphysics many years ago at university. To be honest, a lot of it I found dreadfully tedious at the time but now, in later life, I have come to appreciate one of my tutors who always demanded of us – ‘De omnibus dubitandum’. All things must be questioned. His drive was not to create students who could regurgitate taught subjects for essays but to develop in each of us a questioning mind. I think today, in the age of social media and putative ‘fake news’, a questioning mind is so important and necessary. Unless we question, we shall never look up from our phones or tablets to see what is around us or to challenge the views of politicians and so called ‘celebrities’ and ‘influencers’. A banknote collection is good to review and question. Is this the best note for me? Is this going to fill a long-standing gap? Is this note to be shunned when in such a high grade? Questioning can help us develop and improve not only our minds but also our collection of banknotes.