To live with people, you need to know what they are like. One handy method is to identify the type of person someone is.
The most thorough attempt to sort people into types has been the work of Katharine Briggs and her daughter Isabel Myers. I have written about the Myers-Briggs Type Indicator on my ‘Michael Scannell’ website 
, and I may well return to that wonderfully helpful typology on this site.
But many individuals have their own rough and ready classifications, and I want here to talk about three “types” of another kind altogether. They cut across every systematic typology, and they are easy to recognise. What is more, they are of daily use.
‘Young souls’ and ‘old souls’
The original theory behind this distinction comes from belief in reincarnation. The population of the world keeps increasing, so “new souls”, who have to find out everything for themselves, are constantly being born. Other people may be returning to a world they have lived in, again and again, for centuries, so their souls, “old souls”, know what’s what. In between there will be degrees of ‘youth’ and ‘age.’
You don’t have to believe in reincarnation to find this distinction useful.
In particular, it helps to recognise old souls, who seem from an early age to recognise things as they are, without apparently needing to make an effort. They accept the things they can’t change, and change the things they want to change, without needing the famous prayer to help them distinguish the two. They have an “uncommon common sense.”
There are, in the nature of things, many more young souls, who may be highly intelligent, but have to keep learning from their mistakes. (Like me.)
‘Glass half-empty’ and ‘glass half-full’ people
For young souls, the same situation can be defined, or experienced, differently. (An old soul will simply see what’s there, and what can be done with it.)
In the nature of things, anything which is half-empty is also half-full. But no one who, without reflecting, sees a glass as half-empty, likes the idea of its being half full. And vice versa.
I have seen accounts of this type-distinction associate the first with pessimism and the second with optimism. But those are words for expectations. Optimists expect things to go well; pessimists expect them not to. Whether a glass is half-empty or half-full is a matter of immediate experience: of how things are at the moment. It’s matter of habits of interpretation. (See ‘Creatures of Habit.’ )
When we use these expressions about people, we are talking about their most intimate habits.
‘Owls’ and ‘larks’
This distinction marks a difference between people’s “circadian rhythms.” Some of us wake up full of energy, but lose it as the day progresses: therefore ‘larks’. Some of us find we are at our best in the evening: therefore ‘owls’.
This is not a trivial distinction. Businesses and partnerships (including marriages) can run aground if larks and owls have to do particular things together. What is more, the difference is almost certainly genetic. It needs to be recognised by everyone involved.
(There are, of course, some people who are full of energy both first thing and late at night. In a long life, I have only met two of them—and one of them only gets full command of his powers in the morning after a (very) big breakfast …)