I was wondering if I only have two vectors, then are they affine independent by definition?
The affine independence definition is the following:
$M=\{v_1,v_2,...,v_m\}$ vectors are affine independent if $\{v_j-v_1\}_{j\neq 1}$ are linearly independent.
So, if my set $M=\{v_1,v_2\}$, then we only have $v_2-v_1$, so can we say $v_2-v_1$ is linearly independent? (to what?) So I guess affine independent need at least 3 vectors?
The answer is yes unless $v_1=v_2$.
A subset $M=\{v_1,v_2,...,v_m\}$ of a vectorial space is linearly independent if $\sum_{j=1}^m\alpha_jv_j=\bar{0}\iff\alpha_i=0\quad\forall i\in\{1,\dots,m\}$, so if you only have $M'=\{v_2-v_1\}$ then if we have that $\alpha (v_2-v_1)=\bar{0}\iff \alpha =0$ it implies $v_2\neq v_1$. I can think of the linear space $\mathbb{R}$ where there's only one element in a base and is linearly independent.
Sorry for my bad english.