Before anything else: I am not a clinician and this is not a diagnosis. If you want to know whether you are depressed, the person who can tell you is a doctor, and that appointment is a much smaller thing than it looks from here.

What I can offer is the distinction as I had to work it out for myself, because I spent about a year not knowing which of the two I had and using the uncertainty as a reason to do nothing about either.

Why they get confused

They overlap heavily and each can produce the other.

Prolonged loneliness is a well-documented risk factor for depression. Depression reliably causes social withdrawal, which produces isolation, which deepens the depression. So a man three years into either will often present with a good deal of both, and the question of which came first can be genuinely unanswerable from inside.

That is not a reason to avoid the question. It is a reason to hold the answer loosely and to get a second opinion from someone qualified.

The distinctions I found useful

None of these is diagnostic. They are the questions that helped me work out which conversation I needed to be having.

Does company fix it, even temporarily?

This is the most useful single question. Loneliness responds to good company. Spend an afternoon with someone you genuinely like and it lifts - not permanently, but noticeably, for a while.

Depression frequently does not lift. A man can have a genuinely good afternoon with people he loves and feel the same flatness underneath it the whole time, and often feels worse afterwards for having been unable to enjoy it. Flatness that is present even in good company is the signal that this is not mainly a social problem.

Is it about the situation, or about you?

Loneliness generally points outwards. The thought is there is nobody to ring, and it is a statement about your circumstances that would be resolved by different circumstances.

Depression tends to point inwards and to generalise. The thought is closer to there is something wrong with me or nothing is worth doing, and it does not confine itself to your social life - it takes in work, the future, and your assessment of yourself.

Has the pleasure gone out of things you do alone?

Loneliness leaves solitary pleasures intact. You still enjoy the ride, the book, the game, the work. What is missing is anyone to tell about it.

If the things you used to like doing on your own have stopped registering, that is a different signal entirely, and it is one of the ones worth taking to a doctor.

Is it responsive to what you do?

Loneliness moves when you act on it. Restart a dormant friendship and something measurably improves within a few weeks.

If you have genuinely done the social work - the messages, the fixture, several months of it - and nothing has shifted at all, that is information. It suggests the social explanation was not the whole story.

What is the body doing?

Sleep, appetite, energy and concentration are the ordinary places depression shows up, and they are not typical features of ordinary loneliness. Waking at four every morning, or a persistent change in appetite, is worth mentioning to a GP regardless of what else is going on.

Why men in particular get this wrong

Two reasons I noticed in myself.

The presentation is often irritability rather than sadness. A lot of men do not experience the low mood the questionnaires describe. They experience a shortened fuse, a flat greyness they would describe as being tired, and a withdrawal into work or the shed. Because none of that matches the picture of depression they carry, they rule it out without ever asking anybody.

The social explanation is more comfortable. Loneliness is a circumstance. Depression feels like a verdict on the man. Given the choice I reached for the more flattering explanation and stayed there for a good while, and I do not think I am unusual in that.

Where the line is, plainly

I write about the friendship drought because it is the thing I went and worked on, and because for a lot of men it is genuinely the whole problem. A man whose circle emptied through relocation, a folded team and a decade of not paying attention has a social problem, and social work fixes it.

But that is a narrow claim and I do not want it doing work it cannot do.

Go and see a doctor if: the flatness is there most days for more than a couple of weeks; it is there even in good company; things you used to enjoy alone have stopped registering; your sleep, appetite or concentration have changed and stayed changed; you have done the social work and nothing has moved; or at any point you have thoughts of harming yourself.

That last one is not a sliding scale. It is the point where nothing else in this article applies.

If you need someone now: in the US or Canada, call or text 988. In the UK, Samaritans is 116 123. In Australia, Lifeline is 13 11 14. Anywhere else, findahelpline.com will give you the service where you are. If you are in immediate danger, use your local emergency number instead.

The thing I would say to myself two years ago

Going to the GP was not the large event I had built it into. I had a back complaint that got me into the room for four years before I mentioned anything else, and when I finally did, the conversation took about six minutes and nobody was surprised.

You do not need to have worked out which one it is before you go. Working it out is the doctor's job, not yours, and turning up undecided is a completely normal way to arrive.

If the answer turns out to be the social one, the method for that is here, and what the research actually supports is here.