Motorcycle Safety & Driveability: Replace one tire or both?, motorcycle, tyres

Question
My bike's back tire has plenty of tread left but the front
has barely any tread left.

I've been hearing that if you need to replace one
motorcycle tire you should replace both, but not from
anybody unbiased and levelheaded.

Then I've also heard a few random forum posters mention
that you can only use the same type of tire, and others who
say you can use any combo that works.

What's your opinion and the rationale behind it?

Answer
Sorry for the delay, been away.

Tyres ?

I always keep to the same make of tyre, whenever I change my tyres.  So if your back tyre is alright, choose the same make for the front.  Which tyre do you have fitted at present

My resaon for my choice, is tyres are all very different in character, grip, feel, etc.  I was running Birdgestone 020, but now run the 021 versio.

Hope this helps.  I do have a friend who used to work for Goodyear who did this for me:
http://advancedmotorcycletraining.blogspot.com/search?q=tyres

Regards

Nigel