How many sentences are there in these examples?

• He said "I like pie. I also like tickles."
• He said "The pie cost me £2.30."
• I like pie
• Who watches the watchers?

Some will argue that something like "court martial" is a single word, despite having a space in.

And then there are all those pesky non-European languages. Apparently Chinese uses the same space between words as between characters.

So the answer is "probably not", in the general case.