Can we use though and although interchangeably? Somebody told me that the difference is that though cannot be used at the beginning of a sentence. Is that the rule?
Though can definitely be used at the beginning of a sentence, and has a long history of doing so. Consider Isaiah 1:18 from the King James Bible:
TheFreeDictionary.com cites this usage rule:
However, this seems overly fussy and prescriptive. Consider the following:
Those sound to me like perfectly fine English. They would be perfectly fine using although as well. That, to me, feels like interchangeability, pure and simple. In fact, I can think of no examples in which though cannot be used interchangeably with although. Though your mileage may vary.
As conjunctions, although and though are interchangeable. Although is generally considered more formal than though, though both forms appear regularly in both formal and informal writing.
Though is also an adverb, meaning however or nevertheless. In this sense, though is not interchangeable with although, which is only a conjunction.
And in these examples, though is an adverb and hence not interchangeable with although:
In fact, “though” came before “although.” In the 1300s, before “although” became one word, it was two words —“all” and “though”— with the “all” there to add emphasis to “though (5, 6).”