The subordinating conjunction “though” (and its formal cousin “although”) can be a bit tricky for writers.
Although there is some disagreement, when a dependent clause (such as the preceding) occurs at the start of a sentence, a comma separates it from the independent clause that follows.
The uncertainty arises when that same dependent clause appears later in the sentence, possibly in the middle or at the end. Introduced by a subordinating conjunction rather than a coordinating conjunction such as “and,” which would require a comma, this dependent clause may or may not strictly call for one.
Most authorities seem to think that it should reflect the level of contrast that is intended, i.e., to what extent can the second part be seen as negative while the first is positive or vice versa. For those who allow that a comma may be appropriate, it is the strength of this contrast that seems to determine whether such punctuation applies.
“Although” and “even though” do both
Subordinate and join
Contrasting thoughts to main idea;
For strength of difference, coin.
With comma taken in exchange,
“Though” tells of contrast great,
While “even though” will oft not work
Unless emphatic state.
But then a comma it demands,
Such labor never free;
Akin to “though,” and like “although,”
Much contrast is the key.
Expect a subject and a verb
In construct coming next:
“The message shared was deep and true,
Although ‘twas brief in text.”
Across no contrast or just mild,
A payment is withheld:
“She likes an ice-cream sandwich soft
Although it tends to melt.”
No comma there was warranted,
But look at this instead:
“Outside it's snowing, even though
The day is bright, sun fed.”
Since “even though” inherently
Emphatic contrast brings,
It rates a comma usually,
Regardless what it sings.