How would you articulate the difference between allies and partners?

Allies have a common goal; Partners have a common task to complete.

First, you have to define the question, because it's like arguing if the United States is a"Democracy" or a "Republic" because the answer is 'yes' to either depending at which level you're asking about or in which context (Type of political system? Implementation of a social-political system? Form of governance?)

Historically that view from an international relations view depended on the formality of the relationship, but in the past years the terms have run together or used together (it always seems that our State Department talks about "Allies and Partners" instead of one of the other).

From DoD's view, allies are countries with which we have formal, long-term relationships built on shared values and common forward momentum. Partnerships usually focus on something mutually beneficial during a specific amount of time or for specific circumstances. In this context, our relationship with Ukraine is a partnership.

CPT (Join to see) COL Randall Cudworth Col Lyman Faith CPT Jack Durish Lt Col John (Jack) Christensen
Comments?

IMO Allies are the result of a treaty obligating the US to support another nation-state diplomatically, militarily, with information (share intel), or economically. I view a partner as more of an executive handshake. Not necessarily a paper agreement. The Senate gets involved in treaties, so they are much more formal, and allies are carefully considered from several points of view before a treaty is ratified. Partnerships don't Constitutionally require the Senate to act. Based on this point of view Ukraine may be a partner, but not an ally. Certainly not a NATO Ally.

I don't know. I've never really had either.

I would have challenged your response to the Captains. Allies are those with which we have formal defense agreements: NATO, Japan, ROK, Australia/AUKUS, etc. Partners are those we have informal agreements with, which are usually more focused in scope: Singapore, India, Saudi Arabia, Pakistan, and Egypt were the classic examples, but Ukraine is now the one foremost on our minds.