Well, yes, it is OK. And, on occasion, it can also be very useful.
And yet, about once a month, someone challenges KiwiStreet’s use of this humble connective conjunction. Almost without exception, the authority for their challenge is some all-but-forgotten high school English teacher.
It does not reflect well on the teacher. Nor does it reflect well on the teacher of the teacher. Good writers have been starting sentences with ‘And’ since at least Anglo Saxon times. The King James Version of The Bible makes frequent use of And. And so did Shakespeare.
Many teachers also seem to have convinced their pupils that ‘but’ has no place at the beginning of a sentence. But, again, there is no reason why it should not be used to start a sentence. Indeed, ‘but’ can be a very useful word with which to introduce a balancing statement. ‘All Animals have Sense,’ John Locke noted way back in 1690. ‘But a Dog is an Animal.’
I am not suggesting that you disregard every grammatical ‘rule’ that you learned at school. Some supposed rules do play a useful part in ensuring clear, concise communication. But many do not. Many are just the quirky personal preferences of fuddy-duddy pedants. Those ‘rules’ you may safely ignore.