A weird one this, but I’ve seen it a fair bit, so thought it deserved a few lines.
As a writer, you must be authoritative. You might not be an expert in the subject about which you are writing, but for the duration of those 800 or 1,200 words, you need to act as if you are. Readers are generous: at the start of an article, they have absolute confidence in you. Your task is to never allow this to waver.
One of the ways some new writers erode this confidence is by admitting to lack of research or by implying, often inadvertently, that they’re ignorant of the facts.
“I suppose it could be that… or it’s possible that…”
“This writer hasn’t checked the full details of the case, but …”
“Who knows – perhaps it’s something to do with…”
These sorts of expressions are unlikely to have a place in any non-fiction work, but I see them not infrequently.
I don’t feel you can speculate about something unless you are certain the issue is in doubt. So in my view you first need to check whether or not it is. By all means speculate reasonably about the year in which an old building was built – but only once you’ve confirmed with the local historian that nobody knows for certain when that year was.
So, if it isn’t known, say so – and by all means discuss the possibilities.
If it is known, then obviously just state the fact.
But if you can’t find out whether the answer is known or unknown, it’s probably better to omit mentioning it at all. If you get it wrong, you can bet your bottom that a reader will pounce to correct you on the letters page. Good for the letters page; neither here nor there for the editor; not good for you and your reputation.
Ultimately, it boils down to doing your research. Often, you need to dig deeper into your subject than you might think. This may mean you end up with enough material for a 5,000-word article when you’re only writing a 1,200-word article. But that’s the writer’s life – and that extra material will come in handy one day, trust me.