Possibly probable, perhaps

A funny word, ‘probably’, though we use it daily without a thought. We usually mean “I expect so” or “shouldn’t wonder”. But, as anyone can see, it’s an adverb formed from the adj ‘probable’ - which we often take to mean ‘likely’ - which is another curious word.

But ‘probable’ actually means ‘able to pass a test’ - perhaps ‘worth testing to see if it’s OK’. It is derived from Latin vb probo/probat-- = to ‘approve’, to ‘announce that something has passed the test’. We get our words prove and approve and proof from it - and they are all to do with testing. If you ‘demand proof’ you are requiring a demonstration that a statement or a theory passes the test of thorough scrutiny.

‘The exception proves the rule’ does not mean ‘The exception demonstrates that the rule exists’; nor, as some people have thought, that it shows the rule is too strict: it tells us that the exception tests the rule and shows that it is valid.

‘80% proof’ means that a mixture of distilled spirit and water has been tested, and found to be 40% pure alcohol (ie the standard 'proof' proportion is, in USA, 50% water, 50% alcohol - in UK, a little more alcohol and a litle less water). ‘The proof of the pudding is in the eating’ means that to eat it will be a test of its quality. The 'proofs' of a book or written article are the first printed sheets that are to be 'tested' by a proof-reader to ensure that they are correct before the main print-run begins. ‘Probation’ is a period of testing or trial. ‘Probity’ is the possession of well-earned ('proven') public respect.

And our word ‘probe’ means ‘test’ - to poke something to see what happens, to test it, to show it’s OK. If you receive something ‘on approval’ it allows you time to test it before you buy it. Approbation is a sign that someone or something has passed the test of your - or the public’s - assessment.

So ‘probably’ is rather a cautious way of qualifying your acceptance of a statement: sort of “I’m not saying it isn’t true, but it needs to be tested and verified (maybe perhaps probably) before I accept it”.

Possibly probable, perhaps