Terraforming Mars · Board game rules
Can I play a card if I don't have the required resources?
Quick answer
No, you must pay the card's cost in full before playing it. [p.9 — A) Play a card from your hand]
Details
When playing a card, you must first check the requirements (which relate to global parameters, tags, or production levels), then pay for the card before you can perform its effects. [p.9 — A) Play a card from your hand] The cost is stated in the upper left corner of the card.
You may use steel to help pay for building cards (worth 2 M€ each) and titanium to help pay for space cards (worth 3 M€ each), but you must still have enough total resources to cover the full cost. [p.9 — A) Play a card from your hand]
If you cannot afford a card, you cannot play it. However, you can use the "Sell patents" standard project to discard cards from your hand and gain M€ if you need more currency. [p.10 — B) Use a standard project]